Your "sources" within T-mobile are as useless as texting devices are to a man with no arms.
1) No way we can have it by Sept or before 2009 as AT&T has exclusive Bold rights which is the typical 90 days, but I hear they may have 180 on this one.
2) to answer the question:
Outside of the exclusivity rights (read above) Tmobile's 3G in the US runs on a different band than out in the UK. Tmo back in (don't even remember the date now) bid and won on the 1700mhz (a non-world standard) so the 3G runs of 1700/2100mhz. That does not match up with ATT or Euro/Asia standard which means it's incompatible.
Long story short, no version released of the Bold support our 3G. There's a lot of finger pointing as to whose fault it is since ATT stepped in with the odd frequency choice of their own many years back (850/1900) and basically rushed into the 3G game, but at the same time if we all waited on Deutche Telecom (Tmo's parent company), CDMA carriers would've been the only 3G game in town (US) until now so.. (Devil's Advocate on that one)
3) ANY 3G bb we may possibly get in the future would need to have our band, which no other carriers in North America carry at this time, so RIM would have to put in our special 3g chip which they could only sell to Tmo customers (though I hear a Canada bid will be going on eventually). We may have this friendly little community, but end of the day RIM is about profit margin. They are a worldwide handset provider.. what sense would it make for them to rush to put out a phone that they could only sell to ONE provider and not even the largest, but the 4th largest, who has a relatively tiny bb userbase, just so they can have 3G in one of a handful of cities? Tmobile hasn't completed their nationwide rollout even. It would not make sense for Tmobile to carry a non-specialized Bold since without support of the 1700/2100mhz, it'd just be a glorified Curve since you'd be forced to use EDGE.
I hope this clears up some of the confusion. Let the rumors die.