HP and Agilent have this type of equipment

They can detect GSM signal and lock the channel band.

Jamming the channel is pretty easy. Just send noise to GSM frequency, and it will jam every communication.You can modify your cell phone and constantly send out large power, then you jam everybody.

It is very hard to lock a particular phone secession and jam it. The GSM voice channel is encrypted, the encryption key is shared between carrier and SIM owner. The SIM code is unique.