It’s not easy to provide a good web-based interface for mobile apps. Despite lots of problems with how their mobile service works, I like the Match.com provisioning interface for the mobile app.  It’s straightforward and visually well designed.  Here’s the web-based provisioning process for Cingular:

Step 1.  Intro.

Step 2.  Select Carrier.

Step 3.  Select Model.

Receive WAP Push via SMS:
Follow the link to Mobile Match: http://mobile.match.com/attfrontservlet/dt?CMD=WEBREG&CODE=672640

Click through to provision:
Enter the following code on the registration page.  Do not continue from this card until after you have submitted the registration form on the web page.
807460
Continue

Step 4.  Activation Code.

Step 5.  Complete profile.