From: Alternageek Technology Podcast > T-Mobile blocks Twitter? (updated)
From: T-Mobile Turns Off Twitter?
"T-Mobile would like to bring to your attention that the Terms and Conditions of service, to which you agreed at activation, indicate “… some Services are not available on third-party networks or while roaming. We may impose credit, usage, or other limits to Service, cancel or suspend Service, or block certain types of calls, messages, or sessions (such as international, 900, or 976 calls) at our discretion." Therefore, T-Mobile is not in violation of any agreement by not providing service to Twitter. T-Mobile regrets any inconvenience, however please note that if you remain under contract and choose to cancel service, you will be responsible for the $200 early termination fee that would be assessed to the account at cancellation."
I’m a T-Mobile customer and testing the issue right now, although I have received sporadic updates as recently as last night. It would be quite astonishing if T-Mobile is blocking an opt-in text messaging service considering how common they are and T-Mobile’s relatively small market share in the U.S. However, it wouldn’t be the first time the company has been at loggerheads with a third party service. Earlier this year, T-Mobile blocked VOIP-based free calling service Truphone, but eventually lost in court.There's an bit more including some responses from twitter on it at the interesting customer empowerment site getsatisfaction.com.
GetSatisfaction.com > T-Mobile Shuts Down Twitter Service for Good?