I'm currently using 2.0rc3.
So this advice is "tailored" for 2.0 try to convert it to 1.2.3 if needed any adjusting.
1. Create port alias
add there these ports: 5060, 5190, 5220, 5222, 5223, 5297, 5298, 5353, 5678, 16384-16403(awful lot of ports at my point of view)
2. Create a rule on wan
pass tcp/udp source any source port any destination wan-address(or use portforwards to get interenal addresses) destination port your newly created alias gateway any logging none
3. Apply changes and try