Okay all you people who want to know about digital mobiles. I worked for 2.5 years in mobile mhone communications. We were developing an interface betweeen analogue and digital mobile phones. As soon as someone would walk into the building, the mobile would use the buildings PABX. Therefore your personal mobile would have your deskphones extension, you could make calls and it would only be a local call throught the PABX..blah blah.
Anyway, all you need to listen into a GSM phone is a $250000 comms analyser. These are suppliedd by HP, Motorola, Ericsson...etc...
No special decryption boxes or anything. GSM is a standard, and to test the GSM transcievers you need a test set. All the GSM ocmms analysers have the standard decryption built in. Analogue phones are a lot easier. You can listen with a standard comms analyser, or any scanning transceiver that can tune on the frequency band between 790-950 odd MHz.
All in all, yes the police could scan you if you had a digital phone. BUT the cost of the equipment alone is a huge proportion of the budget. So I would say that it is probably more likely that the federal police would have this gear, and they only have the money and inclination to go for very big time dealers.
Anyway, that's just some facts mixed with my opinion.
Oh yeah, and one more thing...Yes they do go from base station to base station but the FREQUENCY stays the same. You can pick any one of a number of phones out on that frequency. And your phone does send an (encrypted) ID which can also be easily picked up (with the correct hardware) so if they know your phone ID they can tap your phone no matter which frequency or TDM slot you are on. Of course this is what has people concerned about stealing ID's. It won't work if it's digital because if the service detects 2 identical IDs then the service is immedialtely suspended. This ID is transmitted once every now and then when your phone announces itself to the surrounding base stations. It is retransmitted everytime you leave 1 cell and go into another one.
*stopping the endless rambling*
DB
[This message has been edited by Darkblade (edited 07 August 2000).]