receiving tweets but can't send from phone

until yesterday, i have been able to send and receive tweets on my sprint m1 cell phone. now i seem to be receiving tweets without any problem but those i send aren't going through until approximately 12 hours later.

* your Twitter username: hippiechick257

* your country and carrier: USA, Sprint

* SMS previously working? Yes

* Phone successfully verified right now? Yes

* Any response when you send ON via sms? I don't know what this means

* Tweets sent from sms successfully posted on web? Yes

* Do tweets sent by sms show up late on the website? yes, 12 hour delay

* Last tweet successfully posted via sms was: sent 6 May 2009 4:45 pm PT, posted 7 May 2009 5:42 am PT

* Still receiving tweets via sms now? Yes, as of 7 May 2009 2:52 am PT

* If not receiving sms now, last tweet received: 7 May 2009 2:52 am PT