AT&T Pay Per Use Text Messaging = No Texting?

Anyone know anything about AT&T's Pay Per Use Text Messaging plan and the iPhone?

Now that most of my close friends have iMessage I send somewhere in the neighborhood of 5 actual SMS messages a month and want to save some $ by getting rid of the outrageous $20/month Unlimited Texting plan.

Problem is, now that I've dumped the Unlimited Texting plan I can no longer send or receive text messages (iMessage excluded). Anybody know what's up?

I've seen similar problems on AT&T's boards with the problem ending up being "no texting plan was selected" which is BS, I'm on the "Pay Per Use Texting Plan". Just cause AT&T isn't getting $20/month for nothing doesn't mean I'm not on a texting plan. Figured I'd scope things out on here first before raising my blood pressure dealing with AT&T directly.

Thanks.