OK. You're on the right plan and your phone can see the local carriers. Right now all I can say is that there is either some odd configuration error in your account or the local carriers switches aren't communicating with T-Mobile's switch. In either situation the details should be reported to T-Mobile. You aren't by any chance using some ancient Voicestream or Omnipoint SIM? That would be a very unusual situation.
This is one of those cases why I always suggest that international travelers have a "Plan B" for communications. Well, actually you need a plan B for everything but for communications in particular.
