When you receive your first phone call, the Time / Date will be set correctly in my experience. There is a place to enter an NTP server, but it is locked down inside the config. set by WxC.
Various techniques are used to tunnel through your NAT, but the key ones appear to be:
1) NAT Keep Alive
2) STUN Server
However it's done, it works extremely well.
This was something that iTalk could never get sorted during the time I was with them. Calls would not be received in many cases unless you had recently made or received a call. It was all to do with this issue of NAT traversal and obviously there are things that have to be done correctly at the server end, as well as at your end with the SPA2102.
As soon as I switched to VFX, all my calls started arriving even though nothing had changed at my end (same hardware, same software). These guys know their stuff
