sending pics from iphone 3gs

If you don't have a decent 3G network it won't send, if it is larger than 2.1mb it won't send. That's why I suggested increasing the max size allowed.

Your main issue is 3G, if you don't have the 3G symbol by your network it isn't going to send the photo/mms. If you generally have a flaky 3G where you are then wait till your at a better reception area.