I have yet to see any firm evidence of the exact specs of the G2, but that hasn't stopped other websites from posting their opinions. The pictures of the handset we have seen so far confirm a QWERTY slide-out keyboard, and an LED flash, but that is about it. The rest of the features seem to stem from a posting here which may or may not be true.
According to the Engadget article on the story, the phone will have the "model code PC10100 that features support for AWS 3G -- the frequency pair T-Mobile USA uses -- along with 802.11n WiFi. Notably, the filing also points out that HSPA+ is in the cards, which is a feature T-Mobile has been quick to trumpet in its G2 advertising thus far."
CellPhone Signal's article points out that the filing also contains a "Bluetooth 2.1 + Enhanced Data Rate and aGPS receiver."
The phone is being rumored by TmoNews for a possible release on September 29th, thanks to a tipster they contend is well-informed and inside T-Mobile. Stay skeptical, as the haven't given any evidence to back up that claim.
Myself, as well as AndroidandMe, are "hoping T-Mobile will be making some official announcements about the G2 within a week or so."
Image from CellPhone Signal