Never happened before the PR1.3 update and it seems to be happening pretty frequently now which is making me very angry. The text would just stay as pending and never send. Sometimes it will send while it says it's pending and when I receive a text from that person, it is no where to be found in the conversation apps. It's very frustrating wtf is going on? I have T-Mobile by the way.

I'm gonna break this damn phone! Help me

Indeed i got the same problem some time ago, the text is sent, but it says as pending. A solution: remove your "bugged" contact conversation, and REMOVE your contact (of course, type it's number somewhere). Then create a contact again, with the same number, etc. Reboot.
And it should be fixed. I also had that problem only after PR1.3, don't know why. Luckily, it only happened me two times (over the same person... hmm..) Ironically, the person who i text most.

I already did what u suggested before. It also happens to the contact I text the most also...weird...but I'm still having the problem!

Try removing contact, then conversations. Reboot, make the contact again and see if it works. I don't really remember the way i did it, but i got it solved. It's pretty annoying, anyways.

I had the same problem multiple times..what I did was delete that contacts reboot then restore from backup with only "communication and Calendar" selected. .. this work all but one time.. had to restore everything from backup then as my SIM card was no longer recognized... anyway... hope it works for you..