Hey Lardman - The Thunderbolt is one awesome phone and that is - when it works. Mine has been nearly problem free and I rooted it back in January and got a lot more enjoyment out of it than I anticipated. Unfortunately, we had a snafu in our household so I don't have my phone any more but I'm working to get it back.
My husband's Thunderbolt was dropped a few too many times and unfortunately, after replacing the digitizer and a few other parts, several months later the phone has flaked out completely. I swapped SIM cards with him so he would have a phone since I have a corporate and personal phone, then I picked up a Motorola RAZR MAXX but I hate it compared to the Thunderbolt. I've had this new phone for a few days and I'll be taking it back for a refund since I bought it at full price. Meanwhile, I'm out looking for a used Thunderbolt that works and is in very good condition. If your buddy doesn't want to sell you his for your asking price, would you mind asking if he'd be interested in selling to me if his phone is in full working condition? I don't care about the battery. I have an extended battery my husband can't use because of its size and I wouldn't use the standard battery that I already have so I'm all set there. Please PM me if your deal doesn't go through and your friend wouldn't mind working with one of your fellow forum members. Thanks!
If you decide to go through the deal with your friend - I think you'd really enjoy the phone. I want to go back to it as soon as I can. The RAZR MAXX is not nearly as good as the Thunderbolt. Graphics are somewhat choppy looking, widgets are limited, the screen color quality is too saturated and too contrasty in comparison to the Thunderbolt which has one of the most amazing screens available. Plus, the Thunderbolt camera is amazing too (for a phone cam). The MAXX camera lacks all around.
Good luck!