A few years ago when I got my first cell, I found the the vendors had online lists by really grossly defined zip codes.  I collected the number for the following vendors: ATT, Cingular, Sprint, and Verizon.  T-Mobile, my own present vendor wasn't around then.  The gross definition so you will have an idea of what I mean by gross:  Los Angeles included all of the 900nn through 939 and pretty much all of the 213,818,626,707,805,909, 714(and some other area codes my feeble mind doesn't remember just now). Ones like 310 weren't even a dream (310 showed up shortly before I got my cell phone about 1997).

With any luck they're still publishing those numbers online.

Good luck.

Cell phones by cities