Cydia's BiteSMS is probably your best bet, but you're looking at 10-15˘/message to send out ($5 minimum credit buy in) and requires you to have a data package or wifi to use. They will send your ID as your cell phone number, as they confirm your number through a registration text sent to your phone).
I've used Bite's service successfully in the past on a text-messaging-blocked number. Plus buying SMS credits gives you a year of ad-free use of their Texting app.
My common forum nick: GenesisDH.
R.I.P. Circuit City
We are the Bor... the new AT&T: Your World, Assimilated.
1000th post: Sept. 29th, 2008, 17:42 CDT