Did you even look at the OsmocomBB project? It's pretty well-known that the their software (with some alterations) can be used as a poor man's BTS, and so can

Did you even look at the OsmocomBB project? It's pretty well-known that the their software (with some alterations) can be used as a poor man's BTS, and so can passively sniff other phones. They're pretty cagey about it, and understandably so since they're pretty conscientious about complying with laws and regs and yet they apparently draw a lot of script kiddies looking to "hack peoples phones signals". Besides, base stations are available openly on the market now at pretty reasonable prices. It's why I never talk about anything truly private on a mobile phone.