A couple of weeks ago I was messing around with the wireless router settings, and discovered a page called "Wireless Station Access List". This seems to be an an 'approved' list of devices that are always allowed to connect.
The /only/ entry in this page was the Sony phone mentioned in the first post - same name, same MAC. So obviously I deleted the entry.
Tonight I randomly wondered if there was anything showing up on the network (haven't checked since changing that setting). There's no Sony phone showing up. There's an Alcatel 5038X showing up instead.
What. The. Fuck.
https://www.dropbox.com/s/j4tzj7fdjzae6tr/da-faq.png?dl=0