What exact city in So Cal? Service can depend on a lot of variables, the radio frequencies received & transmitted by your phone can be interrupted by everything & anything. Line of sight technology only allows us so much. Most major freeways have towers nearby, but out in the middle of nowhere, TDMA will get better signal because of the effective range of the towers (TDMA 2-5 mi. effectiveness, GSM 1-2 mi. efectiveness of the towers ability to transmit radio frequencies depending on which direction the tower is pointing & the weather.) If you live in a major metropolitan area you most likely will get coverage on GSM.