How to Build Your Own Rogue GSM BTS for Fun and Profit
I wouldn't even think about doing this unless you are in a faraday cage environment or other locked down RF environment where you can be absolutely sure you have complete control over all RF emitted by the device and you know exactly which devices are able to connect.Otherwise, in the US expect the FCC and network operators to become intimately familiar with who you are rather quickly.Having random public phones roam onto your rouge cellular network is a public safety risk (potentially no 911 access) as well as any number of laws being directly broken (unlicensed spectrum use, denial of service to legitimate licensed networks etc).