UKVoIPTalk.com

I would be very grateful if someone could help me. I have a Siemens
SIP phone, and my son has a Voipcheap account which he uses on his
laptop. I too have signed up for Voipcheap, but can't work out how to
configure my phone so that I can dial him on his computer.

It seems I can only dial IP addresses or numbers from my phone. His IP
address is of course behind a router. (He is on a wireless connection
in student lodgings in Switzerland).

Sorry if this is really elementary but I couldn't find an answer on
Google or on VoipCheap. Maybe I wasn't looking in the right places!

Tony