@M

There is no way that a satellite can pickup a mobile phone transmission. I could (just about) believe that they will be able to detect that something is transmitting on the required frequencies. However, a mobile phone system such as GSM doesn't transmit on many different channels. This means that lots of phones, in different cells, will be transmitting on the same frequencies at the same time (hence why there are cells) so a satellite would only be able to pick up garbage as many transmitters on the same channel, but in different cells would talk over each other.

Talking about dedicated taps, such as those which happen as Menwith Hill, is a different matter, though.