Unable to send or receive text messages

I've had major texting issues with my DROID 4. Many of my texts come back with a triangle "Message not sent" error message. It is getting extremely frustrating. I got a new Droid 4 and am having the same issue. I'm not using a third party app. It seems like it's been happening ever since the last software update. I'm in zip code 95366.

Ready to trade in for an iPhone,

Thanks in advance for any suggestions