I use messaging all the time, so I understand how important it is for this feature to work correctly! I'd like to ask a couple of questions to get to the root of the issue.
-Are you using messaging or iMessage with the iPhone?
-Is this happening with all messages, or a specific number of contacts?
-Your post mentions sending messages, Are you able to send all of your messages with no problem?
Please try a soft reset of your device as a troubleshooting step. Follow this link for the steps:
Post back with your results, so we can ensure you're OK. Thanks!
Follow us on Twitter @VZWSupport