If you report the phone lost/stolen they will put the serial number on a list that prevents other people from activating it. Unfortunately, there are ways around that for people who know how to tamper with phones, but for the most part that's all you can do. If the phone has GPS and is turned on, your provider may be able to locate it for you but if it's going straight to voicemail it's probably off.

I know I should be asking my provider this but I thought id give it a shot here first. I recently lost my cellphone and was wondering if there is anyway to block the phone from being used on our only gsm network here in ak (cellone)? There not using my sim coz when i call the number it goes straight to voicemail. Any info would be appreciated.