Sounded like most people affected were East-coast, right? I'm Midwest, so that could be why.
I also read that they were all using the stock messaging app though, too, and people thought it could be somehow tied to some sort of "signature" the stock AOSP/CM messaging app sends it's SMS messages. Didn't see anybody mention if they were using a different texting app like GoSMS, Chomp, or Handcent.
I was using the stock messaging app. I also tried a few others GoSMS and another one and none of them changed the fact that until I did airplane mode on/off I couldn't send a text. once airplane mode was cycled i could send one text.. or when another one came in, then one text.
I live in central PA and had the issue where I could only send 1 sms/mms and had to reboot. I was on the ML1 modem (with MF1 firmware) and what worked for me and others is to go back to a TW rom. Then flash the MB1 AIO firmware. Make sure you can send multiple sms/mms. If they go through, you should be good to use AOSP roms. After doing this, I tried CM11, C-Rom and PacMan and all 3 allowed me to send sms/mms. The key is to stay on the MB1 modem. Don't upgrade to a more recent modem.