Hello opwog,
There are a few ways to isolate this but based on the sounds of things it sounds like something specific to the location. Do you also connect to a WiFi network when you are using this device in CA? Have you considered it may have something to do with the difference in routers or your ISP? Here are some steps to address the WiFi network you're connected to: http://support.t-mobile.com/docs/DOC-5092
If the dropped calls are happening everywhere we would have a different perspective and recommend a master reset on your device. Here are the steps for that: http://support.t-mobile.com/docs/DOC-6205