In 2011, area code 603 was said to be nearing exhaustion and a second area code for New Hampshire was expected to be activated by 2013 as a statewide overlay plan. As a result of changes in allocation policies and a reclamation of a large block of previously allocated telephone numbers, including number pooling, the exhaustion time frame has been moved to at least 2032.
Area code 603 has telephone numbers assigned for the central office code 988. 988 has been designated nationwide as a dialing code for the National Suicide Prevention Lifeline, which creates a conflict for exchanges that permit seven-digit dialing. This area code is therefore scheduled to transition to ten-digit dialing, mandatory after October 24, 2021.
- "Archived copy". Archived from the original on September 29, 2011. Retrieved November 20, 2010.CS1 maint: archived copy as title (link)
- Dave Brooks (18 May 2016). "Area code 603 will reign supreme thanks to technology". The Concord Monitor. Retrieved 17 March 2019.
- "Transition to 10-digit dialing (for 988 as 3-digit access to National Suicide Prevention Hotline)" (PDF). North American Numbering Plan Administrator. January 8, 2021. Retrieved March 9, 2021.
- NANPA area code map of New Hampshire
- List of exchanges from AreaCodeDownload.com, 603 Area Code
- December 2010 newspaper article about then-uncertain future of 603
|West: 802||area code 603||East: 207|
|South: 351/978, 413|
|Massachusetts area codes: 339/781, 351/978, 413, 508/774, 617/857|
|Maine area codes: 207|
|Quebec area codes: 367/418/581, 438/514, 450/579, 819/873|
|Vermont area codes: 802|