Well, let me give you an idea how sophisticated they could easily be: Where I live (netherlands) we have a whole bunch of cell phone operators and they all cell their phones together with subscriptions based on sim-lock. These sim-locked phones are usually pretty expensive models sold at a great discount, so there is now a cottage industry of sim-locked phone unlockers.

These people are all at about the same level of tech as the satellite code crackers a couple of years ago, and it isn't rare to see top of the line scopes, all kinds of specialized soldering equipment (including vacuum smd soldering stations) and laptops full of software geared towards getting a cell phone to do something it really doesn't want to do.

This involves forced firmware upgrades, replacing chips on the board (usually eeproms or flashed chips with blank ones to be able to trick the firmware into thinking it is on a new, unused phone).

If any one of these guys gave a seminar for a week or so the 'bad guys' would be in the possession of all the knowledge and gear they would need to do just about anything they wanted, short of rewriting the phones OS completely. And they wouldn't need that because in their world simpler is better, and writing software is a complicated business.