Twitter (click to follow me) is a social networking phenomenon and powerful communication medium; it's shown vast growth and currently has almost 700,000 users. With these facts in mind, I was disappointed to hear that T-Mobile is blocking Twitter, since (unfortunately) I'm a T-Mobile customer and frequent Twitter user.
When considering failed IT, whether software implementation problems, web sites that don't work, or wasted government dollars, it's tempting to focus first and foremost on technology. However, the reality is most IT failures are rooted in the human dimension.
In this case, Twitter stopped working on a T-Mobile customer's phone, who called tech support for assistance diagnosing the problem. Turns out there was no technology issue. Instead, the customer interpreted a new T-Mobile business policy as technology failure. Such policy / technology confusions happen all the time.
My own view on why T-Mobile is blocking Twitter: the company sees an opportunity to extract transport fees from Obvious, the company which owns Twitter. This raises interesting issues, since Twitter transmits its messages over standard SMS, for which customers are already paying. This story is not over and will have net neutrality ramifications if T-Mobile pursues the issue to conclusion. Get ready for a big fight!
Update (12/15/07, 10:00 pm): Despite initial T-Mobile customer service assertions the problem was business policy-based, turns out it's garden-variety technical failure after all. Seems like T-Mobile has some internal communications issues to iron out.