I'm using a standard linksys PAP2 over an ADSL link for a warehouse cordless analogue phone running in Christchurch off the system in Auckland. Seems to run really well. It is the only phone/ device on the end of the VPN link most of the time except one PC doing RDP back to Auckland too..
Running IP500V1 with 5.0.8 and yes, SIP endpoint license required for SIP extensions. 8)
There are docs on the knowledgebase site and partner portal about sip extensions. Usually just need to get the user login details right in telephony tab. ie login code.
Disable the built in * codes, feature codes built into the ATA if possible. that can cause dramas and conflicts with existing Avaya short codes.
Chris