Unfortunately, I haven't yet managed to get a PPP link going to the camera from Linux; pppd doesn't want to connect, and when I connected to it with minicom (a serial terminal app), it just responds with "OK" to anything I type. The options are (a) there's a magic command which starts a PPP session on the camera's built-in server, or (b) it needs a username/password via PAP or somesuch.
(Once PPP is going, it'd be interesting to portscan the camera; perhaps there's a port which gives a shell on whatever embedded OS the thing runs?)
Update^2: It appears that the camera software adds an entry to Windows Dial-Up Networking for connecting to the camera; this reveals that the camera imitates a modem, waiting for two commands (SV, and then ATDT1234567), upon which it starts a PPP server. Now, the problem is, I so far haven't managed to get pppd under Linux talking with the camera's server at all; it just times out.