I've never seen a 1 in front of the area code. The telco does not send it because it's not a supported format. The vast majority of phone systems must see 10 digits with the delimiters or it will reject CID info. If you want the 1 then on some systems you can program it to insert 1 on out of area incoming strings. This of course can be an absolute mess in some areas with mixed local and long distance in the same area code with multiple office codes.

T1 or PRI circuits will fail on incoming if the format isn't *ANI*DNIS* with ANI=to 10 and DNIS=to digit length programmed in your system.