The change is being made so Connecticut can have two new area codes, 475 and 959. The state's 203 area code is expected to run out of numbers in the middle of 2010. The 860 area code will run out in 2011.
Callers can begin dialing 10 digits for local calls beginning in April, but the longer number will be mandatory in December.
State officials say no existing calling areas, rates or charges will change.
NEW YORK AND TRI-STATE AREA NEWS