I got in more testing of the service early this week than I thought I would, so 2 days ago I put in the request to have my old number transferred. This morning, I received an email saying that there was a road block in the process (distinctive ring service on the landline), and that I needed to remove that and call them back with a confirmation number to continue the transfer.
11:40 - Email received from Vonage
11:45 - Service order submitted to AT&T
11:55 - Completion confirmation email received from AT&T
Nearly an hour later, and I'm still trying to call Vonage to tell them that it's done, but no one's picking up. I'm hoping they don't have any more opportunities to impede their own progress like this...
12:55 - Reached someone at Vonage about the transfer