Everything is speculative until the new iPhone comes out, but...
- The new iPhone, if unlocked and activated using an alternative technique (e.g. Pwnage), would work on EDGE (but not HSPA) with T-Mobile USA.
- It is widely expected that Pwnage will be able to unlock both the 3G iPhone and 2.0 firmware, but perhaps not immediately after they are released. It's pretty widely expected, also, that the other tools such as Zibri's tool will also adapt. When 2.0 comes out, you may not be able to use it on the day of release on an unlocked iPhone, but it should probably be available to you fairly quickly.
- The principle advantages of the new iPhone if you use T-Mo USA would be better resale value and longer battery life and GPS, I guess.
- The new iPhone is expected to be a *lot* more expensive than the current one, at least initially, on the used market, because unlike the current one, pretty much everyone who buys one is going to get saddled with a contract and ETFs of some kind.
- With all that being said, I'd personally say that you're better off getting a used iPhone current gen, as long as you don't get excessively beaten up by markups -- if you can get anywhere near the refurb prices (e.g. $250US for 8GB), go for it.
