HUNTSVILLE, Alabama - The new 938 area code has been in effect for almost 18 months, but you've probably never used it.

The new area code was laid over the 256 area code area in 2010, leading to 10-digit dialing across North Alabama.

Officials can't say how many numbers with the 938 area code are in use, only that 20,000 numbers with the 938 area code have been reserved by an Internet provider.

About 800,000 numbers remain available in the 256 area code, John Manning, senior director of the North American Numbering Plan Administration, said Tuesday afternoon.

The Alabama Public Service Commission decided to overlay a new area code over the geographical area served by the 256 area code instead of splitting the geographical area, as happened in 1998 when the 256 area code was split off from the 205 area code.

The 938 area code went into effect July 10, 2010. To prepare telephone customers for the change, the Public Service Commission about a month earlier implemented 10-digit dialing for all calls in the 256 area code.

The changes were necessary because most of the phone numbers in the 256 area code had been assigned, primarily because of the proliferation of cell phones.

Although 800,000 unassigned numbers remain in the 256 area code, officials said they can't wait "to hit the wall" before starting a new area code.

So far, only SBC Internet Services has been assigned any prefixes in the 938 area code, according to the North American Numbering Plan Administration, which oversees the numbering plan for telephones in the United States and its territories, Canada and the Caribbean.

SBC has the 223 exchange in Red Bay and the 238 exchange in Goodwater reserved in the new area code. Each exchange represents 10,000 telephone numbers.