Happened again.

It seems that the issue is when I lose my signal in the midst of enabling the service.

I finally got someone on the phone to agree with my assessment, and who knew of a similar problem with buying ringtones.

Also, they have no way to expire the service early, either in the technical support, billing, or customer service departments. He did suggest that it could be reset by canceling the account and opening a new one, but that I might lose my phone number. Since I exclusively use my Google Voice number, this wasn't a big deal.

He transferred me to customer service, where I was transferred to a phone that, as it turns out, the rep forgot to log out of when she went to the bathroom. So I waited for five minutes or so for her to get back to her desk.

Once she came back, she tried a couple of things short of canceling the account, none of which worked. Then she canceled the account and asked "Is there anything else I can do for you today?" Uh, yeah: activate my phone. So I gave her the SIM number and IMEI, she put me on hold for a minute, then came back and said there was a problem and that they'd have to call me back in about 30 minutes. It's been about 45 minutes now.

So now, not only do I not have internet service, I also don't have phone service. This is working out really well.