Phone as Modem

EDIT: just read the "What This Thread is For" post...since this is a question maybe it's in the wrong place.  My apologies.  Please move if necessary. 

Looking for some help with a Sprint Touch Diamond as a modem.  I used my Treo 700 as a modem all the time without any trouble.  I've tried connecting with the Touch's Internet sharing application and get an error such as "remote device disconnected," or "user name and password are incorrect."

I went to Sprint's website to try and find some answers and what I found seems to indicate the phone isn't compatible.  It doesnt' show up under the phones that are compatible with the Phone as Modem add-on.  Isn't that an advertised feature of the Touch Diamond?  Then I looked at the Simply Everything plan that I have and it says Phone as Modem isn't available at this time.

What? 

I'd been using my Treo as a modem for 6 months with the same plan. 

Tried calling Sprint but was on hold for too long and figured I'd have better chances here!

Thanks