I've noticed that when I try to send a text message and I'm either receiving another text or an imcoming call, that I receive an error message: "message not sent"
But the Droid X doesn't automatically resend.
Unfortunately the Droid X does not resend the text messages that failed due to an incoming call or text message. You have to resend the message manually. I know this can be frustrating and I apologize for the inconvenience.