OK...have managed to get it to work - the problem is caused by routers with firewalls built in, as certain ports need to be open/forwarded.

What I did first was turn off the router's built in firewall. I then configured my Netgear router to assign a static IP to the 770 each time I connect - I set it as 192.168.1.5

I then followed the instructions from this port forwarding site here

Select your router and then select 'Gizmo project' from the list of programs and then follow the instructions to forward ports 5004, 5005 and then 64064.

When someone calls my IPKALL Washington number it now rings on my GIZMO and I have sound both ways. There's a tiny delay but overall - its great. (and its FREE). So now I receive calls via IPKALL which I configured from my log-in page on IPKALL.com using the SIP number (without the dashes etc. Just 1747xxxxxxx from the account profile page on Gizmo) and the proxy of proxy01.sipphone.com. I disabled voicemail on IPKALL as well seeing that Gizmo also has it and I dont need two.

Dump the callwave number - its not worth the hassle.

Have Fun!!