How to create a portable GSM BTS which can be used either to create a private ( and vendor free! ) GSM network or for GSM active tapping/interception/hijacking … yes, with some (relatively) cheap electronic equipment you can basically build something very similar to what the governments are using from years to perform GSM interception.
Adafruit sells working 2G SIMcards for use in telephony enabled projects. hacking hardware The manufacturer/provider is Ting. GSM Pay as you go provider, kind of like voip.ms.
howto build a personal gsm cellular network using linux, a RasPi, and an SDR.