With the 203 area code expected to run out in 2010 and the 860 area code in 2011, residents of Connecticut will be getting two new area codes. Next month, a 475 area code will begin to be distributed and after the 860 code runs out, 959 will be introduced.
Along with the new codes comes mandated ten-digit dialing, which includes dialing the three digit area code for all calls made in Connecticut. Callers can start dialing the extra three digits on April 1st, but the rule won't be a requirement until the 1st of December.

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For updates on when 203 and 860 are expected to run out of numbers, you can go to http://www.wherecall.com/AreaCode-Exchange/203.htm (for 203) and http://www.wherecall.com/AreaCode-Exchange/860.htm (for 860). NANPA, the organization that does the estimates, updates the estimates twice a year (they are due to update again in April).
-Scott