Cellular module

The installer of my system locked out my panel, and refused to give me the installer code. The rep of the service provider I planned to use said that I could install a cellular module to bypass the installer code. Just wanted to confirm this with the folks here to see if that's a good way to proceed. Here are my questions: 1. Does this sound like a good idea to you? 2. I am on a pay-as-you-go cellular plan. Would that work with cellular monitoring? 3. Will I be able to program my system from the keypads? What features provided by the panel would be lost by switching to this cellular module? Thanks.