That red triangle means exactly that Is this still happening? If so, are you in an area where there is T-Mobile coverage? Also, did you get a chance to try and power off your device for a few seconds and then power it back on?
Happy Wednesday, lchinitz!
I'm just stopping by to see if you're still getting an error symbol when sending texts. If you are, please take a look at the above questions that Chris asked so we can get a better idea of why this is happening.