New Hampshire, United States
Eastern Time
3:11 PM
Area Code
603
State / Province
New Hampshire
Country
United States
Time Zone
Eastern Time
Area code 603 covers 147 cities and communities across New Hampshire, based on telephone company rate center data.
Use the E.164 format for clickable phone links (RFC 3966):
<a href="tel:+16035550100">+16035550100</a><a href="tel:+16035550199">+16035550199</a>Look up which exchange in New Hampshire a specific 603 number is homed to, and whether its block is wireline or wireless. See what a reverse lookup can establish before relying on the answer.
752 active prefixes in this area code, assigned as 5,810 thousands-blocks — pooling splits one prefix across several carriers, so each block is listed separately with the rate centre it is homed to, its carrier of record, and the switch that serves it.
Showing blocks 1–100 of 5,810
| NPA-NXX | Block | Rate centre | Type | Carrier (OCN) | Switch | LATA | LIR | Dates |
|---|---|---|---|---|---|---|---|---|
| 603-200 | 0 | Newmarket | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
| 603-200 | 1 | Newmarket | Landline or VoIP | TELNYX LLC (073H) | MNCHNHCO23Z | 122 | — | — |
| 603-200 | 2 | Newmarket | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
| 603-200 | 3 | Newmarket | Landline or VoIP | MCIMETRO ACCESS TRANSMISSION SERVICES LLC - NH (7778) | MANCHESTER | 122 | — | — |
| 603-200 | 4 | Newmarket | Landline or VoIP | MCIMETRO ACCESS TRANSMISSION SERVICES LLC - NH (7778) | MANCHESTER | 122 | — | — |
| 603-200 | 5 | Newmarket | Landline or VoIP | TELEPORT COMMUNICATIONS AMERICA, LLC - NH (8299) | DOVRNHTHXEX | 122 | — | — |
| 603-200 | 6 | Newmarket | Landline or VoIP | TELEPORT COMMUNICATIONS AMERICA, LLC - NH (8299) | MNCHNHCOX1Y | 122 | — | — |
| 603-200 | 7 | Newmarket | Landline or VoIP | TELNYX LLC (073H) | MNCHNHCO23Z | 122 | — | — |
| 603-200 | 8 | Newmarket | Landline or VoIP | TELNYX LLC (073H) | MNCHNHCO23Z | 122 | — | — |
| 603-200 | 9 | Newmarket | Landline or VoIP | TELNYX LLC (073H) | MNCHNHCO22Z | 122 | — | — |
| 603-200 | A | Newmarket | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
| 603-202 | 0 | Concord | Wireless | BELL ATLANTIC MOBILE, INC (6386) | MNCHNHACAMD | 122 | — | — |
| 603-202 | 1 | Concord | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-202 | 2 | Concord | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-202 | 3 | Concord | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-202 | 4 | Concord | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-202 | 5 | Concord | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-202 | 6 | Concord | Wireless | BELL ATLANTIC MOBILE, INC (6386) | MNCHNHACAMD | 122 | — | — |
| 603-202 | 7 | Concord | Landline or VoIP | PEERLESS NETWORK OF NEW HAMPSHIRE, LLC - NH (927H) | MANCHESTER | 122 | — | — |
| 603-202 | 8 | Concord | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-202 | 9 | Concord | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-202 | A | Concord | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-203 | 0 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 1 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 2 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 3 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 4 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 5 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 6 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 7 | Manchester | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-203 | 8 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | 9 | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-203 | A | Manchester | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-204 | 0 | Nashua | Wireless | BELL ATLANTIC MOBILE, INC (6386) | MNCHNHACAMD | 122 | — | — |
| 603-204 | 1 | Nashua | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-204 | 2 | Nashua | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-204 | 3 | Nashua | Wireless | NEW CINGULAR WIRELESS PCS, LLC - DC (4036) | DRRYNHBC1MD | 122 | — | — |
| 603-204 | 4 | Nashua | Wireless | BELL ATLANTIC MOBILE, INC (6386) | MNCHNHACAMD | 122 | — | — |
| 603-204 | 5 | Nashua | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
| 603-204 | 6 | Nashua | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-204 | 7 | Nashua | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-204 | 8 | Nashua | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-204 | 9 | Nashua | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-204 | A | Nashua | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-205 | 0 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 1 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 2 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 3 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 4 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 5 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 6 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | 7 | Portsmouth | Landline or VoIP | CENTURYLINK COMMUNICATIONS, LLC (508J) | MNCHNHCO16Z | 122 | — | — |
| 603-205 | 8 | Portsmouth | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO46Z | 122 | — | — |
| 603-205 | 9 | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-205 | A | Portsmouth | Wireless | OMNIPOINT MIAMI E LICENSE, LLC (6889) | MANCHESTER | 122 | — | — |
| 603-206 | 0 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 1 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 2 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 3 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 4 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 5 | Manchester | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
| 603-206 | 6 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 7 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 8 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | 9 | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-206 | A | Manchester | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO45Z | 122 | — | — |
| 603-207 | 0 | Derry | Landline or VoIP | TELNYX LLC (073H) | MNCHNHCO23Z | 122 | — | — |
| 603-207 | 1 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 2 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 3 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 4 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 5 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 6 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 7 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 8 | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-207 | 9 | Derry | Landline or VoIP | TELNYX LLC (073H) | MNCHNHCO23Z | 122 | — | — |
| 603-207 | A | Derry | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-208 | 0 | Lyme | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-208 | 1 | Lyme | Landline or VoIP | COMMIO, LLC (939H) | MNCHNHAC3MD | 122 | — | — |
| 603-208 | 2 | Lyme | Landline or VoIP | PAETEC ITEL, LLC (829J) | MNCHNHCO46Z | 122 | — | — |
| 603-208 | 3 | Lyme | Landline or VoIP | ONVOY, LLC - NH (637E) | MNCHNHCOX9Z | 122 | — | — |
| 603-208 | 6 | Lyme | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-208 | 7 | Lyme | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-208 | 8 | Lyme | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-208 | 9 | Lyme | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-208 | A | Lyme | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 0 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 1 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 2 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 3 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 4 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 5 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 6 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 7 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 8 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | 9 | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-209 | A | Keene | Wireless | UNITED STATES CELLULAR - NH (6290) | MNCHNHCOX4Z | 122 | — | — |
| 603-210 | 0 | Suncook | Landline or VoIP | OTEL TELEKOM, INC. - NH (9827) | PTMONH073MD | 122 | — | — |
| 603-210 | 1 | Suncook | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
| 603-210 | 2 | Suncook | Landline or VoIP | COMCAST IP PHONE, LLC (318J) | MNCHNHIE6MD | 122 | — | — |
Block-level assignments from the North American Numbering Plan administrator, via localcallingguide.com.
Assigned Prefixes
752
Assignment Blocks
5,810
Rate Centers
147
Carriers of Record
51
| Type | Blocks | Share |
|---|---|---|
| Landline | 1,191 | 20% |
| Landline or VoIP | 2,476 | 43% |
| Wireless | 2,143 | 37% |
| Carrier | Blocks |
|---|---|
| CONSOLIDATED COMM OF NO. NEW ENGLAND-NH | 1,059 |
| BELL ATLANTIC MOBILE, INC | 929 |
| OMNIPOINT MIAMI E LICENSE, LLC | 483 |
| PAETEC ITEL, LLC | 468 |
| NEW CINGULAR WIRELESS PCS, LLC - DC | 376 |
| COMCAST IP PHONE, LLC | 324 |
| UNITED STATES CELLULAR - NH | 302 |
| LEVEL 3 COMMUNICATIONS, LLC - NH | 236 |
| FREEDOM RING COMMUNICATIONS, LLC | 221 |
| ONVOY, LLC - NH | 219 |
| 41 other carriers | 1,193 |
Carrier of record for each block. Numbers ported to another carrier keep their original block assignment, so this is not a lookup of who serves a given number today.
| Rate Center | Prefixes | Blocks |
|---|---|---|
| Manchester | 80 | 525 |
| Nashua | 58 | 436 |
| Concord | 39 | 325 |
| Derry | 29 | 238 |
| Dover | 29 | 208 |
| Portsmouth | 28 | 216 |
| Merrimack | 23 | 189 |
| Salem | 20 | 159 |
| Laconia | 19 | 162 |
| Keene | 17 | 165 |
| Rochester | 16 | 128 |
| Exeter | 15 | 125 |
| Milford | 11 | 100 |
| Plymouth | 10 | 67 |
| Suncook | 9 | 93 |
| Claremont | 8 | 75 |
| Hampton | 8 | 48 |
| Hanover | 8 | 53 |
| Lebanon | 8 | 67 |
| West Lebanon | 8 | 77 |
| Durham | 7 | 40 |
| Plaistow | 7 | 47 |
| Bedford | 6 | 57 |
| Berlin | 6 | 55 |
| Littleton | 6 | 51 |
| Meredith | 6 | 51 |
| Peterborough | 6 | 40 |
| Lancaster | 5 | 42 |
| Newport | 5 | 38 |
| North Conway | 5 | 52 |
| Raymond | 5 | 45 |
| Sunapee | 5 | 35 |
| Center Ossipee | 4 | 31 |
| Colebrook | 4 | 28 |
| Conway | 4 | 38 |
| Goffstown | 4 | 42 |
| Hampstead | 4 | 43 |
| New Boston | 4 | 38 |
| North Woodstock | 4 | 33 |
| Seabrook | 4 | 39 |
| Tilton | 4 | 34 |
| Woodsville | 4 | 29 |
| Barrington | 3 | 19 |
| Bristol | 3 | 25 |
| Campton | 3 | 29 |
| Canaan | 3 | 16 |
| Candia | 3 | 31 |
| Danbury | 3 | 19 |
| Deerfield | 3 | 21 |
| Epping | 3 | 25 |
| Greenfield | 3 | 32 |
| Hollis | 3 | 29 |
| Jaffrey | 3 | 24 |
| Kingston | 3 | 30 |
| Lyme | 3 | 23 |
| Milan | 3 | 17 |
| Newmarket | 3 | 23 |
| Orford | 3 | 11 |
| Pelham | 3 | 33 |
| Pike | 3 | 16 |
| Rye Beach | 3 | 24 |
| Somersworth | 3 | 28 |
| South Hampton | 3 | 23 |
| Tamworth | 3 | 18 |
| West Chesterfield | 3 | 23 |
| Wolfeboro | 3 | 21 |
| Alstead | 2 | 14 |
| Alton | 2 | 13 |
| Andover | 2 | 11 |
| Antrim | 2 | 13 |
| Ashland | 2 | 14 |
| Barnstead | 2 | 6 |
| Bartlett | 2 | 13 |
| Belmont | 2 | 14 |
| Boscawen | 2 | 9 |
| Canterbury | 2 | 16 |
| Center Barnstead | 2 | 9 |
| Center Harbor | 2 | 20 |
| Center Sandwich | 2 | 13 |
| Charlestown | 2 | 14 |
| Chester | 2 | 9 |
| Chichester | 2 | 8 |
| Enfield | 2 | 20 |
| Epsom | 2 | 21 |
| Errol | 2 | 8 |
| Farmington | 2 | 17 |
| Franklin | 2 | 11 |
| Gilmanton Iron Works | 2 | 5 |
| Gorham | 2 | 20 |
| Greenville | 2 | 18 |
| Henniker | 2 | 16 |
| Hillsboro | 2 | 20 |
| Jackson | 2 | 17 |
| Jefferson | 2 | 11 |
| Lisbon | 2 | 15 |
| Meriden | 2 | 7 |
| Milton | 2 | 14 |
| Monroe | 2 | 9 |
| New Durham | 2 | 11 |
| New London | 2 | 8 |
| Northwood | 2 | 18 |
| Penacook | 2 | 18 |
| Plainfield | 2 | 14 |
| Rindge | 2 | 19 |
| Salisbury | 2 | 8 |
| Sanbornville | 2 | 15 |
| Spofford | 2 | 15 |
| Sutton | 2 | 8 |
| Troy | 2 | 13 |
| Walpole | 2 | 15 |
| Warner | 2 | 20 |
| Washington | 2 | 6 |
| Winchester | 2 | 15 |
| Bethlehem | 1 | 10 |
| Bradford | 1 | 7 |
| Bretton Woods | 1 | 1 |
| Chatham | 1 | 10 |
| Contoocook | 1 | 10 |
| Dublin | 1 | 8 |
| Dunbarton | 1 | 1 |
| East Conway | 1 | 10 |
| Fitzwilliam | 1 | 10 |
| Franconia | 1 | 11 |
| Groveton | 1 | 9 |
| Hancock | 1 | 7 |
| Harrisville | 1 | 9 |
| Hillsboro Upper Village | 1 | 1 |
| Hinsdale | 1 | 9 |
| Madison | 1 | 9 |
| Marlborough | 1 | 8 |
| Marlow | 1 | 10 |
| Melvin Village | 1 | 5 |
| Milton Mills | 1 | 10 |
| North Stratford | 1 | 6 |
| North Walpole | 1 | 7 |
| Piermont | 1 | 8 |
| Pittsburg | 1 | 6 |
| Pittsfield | 1 | 11 |
| Rumney | 1 | 7 |
| Sullivan | 1 | 8 |
| Twin Mountain | 1 | 6 |
| Warren | 1 | 6 |
| Weare | 1 | 1 |
| West Stewartstown | 1 | 9 |
| Westmoreland | 1 | 9 |
| Whitefield | 1 | 9 |
| Wilton | 1 | 10 |
A rate center is the telephone exchange area a number is homed to. It sets local calling boundaries, and is not the caller's current location.
Area code 603 is a North American Numbering Plan (NANP) telephone area code assigned to New Hampshire, United States. It is the sole area code assigned to New Hampshire, covering the entire state or province under a single numbering plan area.
Yes. 603 is an active North American Numbering Plan (NANP) area code, currently assigned to New Hampshire, United States. It is safe to answer or dial calls using this area code.
Area code 603 covers 147 cities and communities in New Hampshire, including Alstead, Alton, Andover, Antrim, Ashland, and 142 more localities. This is based on telephone company rate center data — the geographic areas carriers use to determine local calling boundaries and to assign numbers when a business or individual requests a phone number in a specific city.
All numbers in the 603 area code observe Eastern Time (IANA timezone: America/New_York). Eastern Time is UTC−5 in winter (EST) and UTC−4 in summer (EDT). When placing a call to a 603 number from a different time zone, check the current local time above to avoid calling outside of business hours.
From within New Hampshire, dial the 7-digit local number directly if calling within the same rate center, or dial 1 + 603 + 7-digit number for long-distance calls within North America. From outside the US or Canada, dial your country's international exit code followed by 1 603 XXX XXXX. The country code for both the United States and Canada in NANP is +1.
Format 603 numbers using E.164 notation as required by RFC 3966: prefix with +1 and omit dashes and parentheses (e.g., +16035550100). This format ensures tel: links work correctly on all mobile browsers and VoIP apps. See the tel: URI formatting guide for complete examples.