I've been getting this occasionally as well. Its random. I'm always in great 3G coverage. So thats not the issue. Sounds like a network issue with VZW.
most times i only have 1-2 bars.. but im pretty sure i still get the error even when i had 3.
and ive NEVER had this problem with my other phones.. I haven't had this for a month lol.. It ALWAYS say it whenever i try to send or receive pictures.. everything else works fine.
My first X didn't do it, but after about 2 weeks, the speaker blew out, so I took it back and exchanged it for a new one and this one has been doing it. I get the error about 5 to 6 times a week. I went back to Verizon and they said that they need to do a factory reset and have me try using the phone with out any apps to rule that out. I am out of my 30 days and so I know if I do warranty it out, I will get a refurb, so I just live with it and just resend the text.
If I were in your shoes, I would go swap it for another one. You have 8 days, they will give you a new one out of the box, try that for 2 or 3 days and see if the issue continues. If so, return for the iphone, if not, problem solved. But with 8 days left, you have time to test and find out.