I read that a while back and built myself a couple of these babies.
Lessons Learnt:
1. Soldering is not as easy as it looks
2. I am not a solder ninja
3. Forget the 9v battery, use a battery holder for 4 AA 1.5v. More juice in the 4 AAs and less heat. After charging the PDA / phone for a while the case will be hot.
4. The altoids tin makes a nice project box