O2 says its xda II will run the Phone Edition of Windows Mobile 2003 for Pocket PC on a 400 MHz Intel XScale processor. It will have 64 MB of RAM and an SD slot. However, it's possible that some of these specs might be changed by T-Mobile in its version.
The xda II will include Bluetooth wireless networking, but T-Mobile's very brief overview of the MDA 2 doesn't mention this.