@swordfish ok I see it was the statemant from mikegioia which was let me think about uk t-mobile.
I see in older post from you that you explain your problem in detail sorry for ignoring that.
It seems you have a strange problem and it is clear that some provider changed something.
Could you determine diffrences between a working raw mms compared to a raw one from N900.

- How big are the messages you try to send? Maybe the size limit is different between t-mobile and other provider and it could be when you use another phone for sending that it has a compression?