Just for the record, I have both my PAP2T as well as my 502(2nd number) online.
I did just take a look at the VPanel for my 2nd line, and although the 502 shows as registered in the ATA, I had to do a manual reboot for it to really register.
Outbound of course, did work before I rebooted. Now it does shows in the panel.
The 502 is set for 1 minute registration and is pointed to the sip server..

The PAP2T sits there and purrs..not a problem.