GSM has horrible security and carriers aren't exactly doing their best to make their networks secure either. A while ago you needed relatively expensive equipment (around $1000-2000) to be able to sniff on the network, but it's now been done with a few very cheap phones. There's a very informative presentation (with video) here. For this to work, you need to be close to the person you want to eavesdrop on however.

We are using the GX420d model from Zebra. You can order these with Parallel port, Ethernet, Wi-Fi or BlueTooth and they also have a USB port. I've used them from OS X and Linux without any problems. There are drivers for the thing, but you can even print using HTTP, POP3 (!) or connect to the printer over TCP and send your raw commands through that. It took me about a day to figure out how they work, but the printer language is quite easy to understand. Documentation is well done, but getting access to the docs is not so easy. The Zebra tech support is quite helpful though, so you can always ask them.

Guys, we've all know that the Goa'uld have been experimenting with nanotech for a long time. No wonder the Egyptian got some of it.