Assuming that you dont have texting while roaming or anything blocked on your account, these are some things that might cause this:
Incorrect number of digits entered. (or putting a 1 before the number)
International number not supported.
If that doesnt help, I might need a little more info. Are you trying to send regular texts or picture mail? Do you receive a text from 9230 with an error message? Can you recieve texts at all?
As far as i know, i do not have any restrictions in my account, It will happens even with ph # that does not have the 1 before the #, and im just trying to send regular text msg to phone # i have stored in my phone, not pic mail. And i don't get any text message back, just after a while trying to send the msg , in the notifications bar will have a msg with an exclamation mark inside a triangle saying undeliverable msg
Ok, so try sending a message to your own number. If that doesnt work then you need to call sprint and ask to get transfered to tech support.
I have the same problem, or similar. It says it delivers the message, but it does not. I just use text+ to text while I'm roaming. I did an useless 30 MINUTES troubleshooting with sprint and they just said its not their fault but the company's they're roaming to.
I would contact Sprint, see if there is any outages in your area. If messages aren't being sent, then chances are theres an outage near you preventing the connection.