This afternoon I got a call from the folks who had spent hours trying to activate the cellular data plan on an iPad. Having called Apple and AT&T didn't help. The frustration level was understandably very high. At the end of the day it boils down to an odd little problem that AT&T never anticipated.
First the interface for activation isn't great at dealing with errors. The cycle would run like this. You enter all the data and submit it. The system doesn't like your physical address and tells you so. When it presents the form with the error it also removes the password you've entered in your last attempt. However it doesn't highlight the password field so you don't know readily it's been removed. Your next submission is rejected for not having a password. Once you fill that in it gets rejected for the address again and around, and around, and around you go.
Having been through things like this in the past I knew immediately what the problem is. Depending on how you look at it the problem is the US Post Office or AT&T's programmers.