Here a few troubleshooting options:
Check the software version on the phone. You can do this by dialing #4357*4357 (#help*help) and look at your s/w version. The latest release for the software is verison VX10KV11. Check if you have the latest software if not you can go down to any verizon wireless store with a tech and they would be able to upgrade your software. Also one thing that i have on my voyager is auto delete set on for the text message. What that would do is delete your text messages after a while so it would stop saying "message inbox full" but if you recieve a pix/flix message that will still stay in your inbox until you delete that yourself. The last thing that could be doing that is if you have alot of videos/pictures/music in your phone without a memory card they may be using all of the internal memory leaving nothing for the text messages to be stored on. If all else fails and you got the phone last christmas you should still be under a 1 year warranty and they would be able to replace the phone.
Hope this was helpfull.
If you have any additonal questions feel free to send me a direct message