siemens gigaset S685IP and S675IP help

Hello everyone :
I have following problem , i have a siemens gigaset S685IP where everything is configured fine and my voipbuster and gigasetnetwork account are showing that they are registered , and a member of my family has a siemens gigaset s675ip where also the conections are showing that they are registered .
Well my first question is ,when i try to call to then from the gigaset network the telephone is calling but bouth sides but we can't hear anything , and they can also call to me , but i can't hear anything. what can the problem be?
And second question is whe have also a voipbuster account how i can call then via Sip with my S685IP or they can call me via Sip from the S675IP? what info i must enter on the phone?
Regards
And Sorry for my poor english

Hi Centralrock and welcome to Voipuser

First part of your question - sounds like a ports issue, you need to open ports in your router for the Siemens equipment. It should explain to you in the manual which ones, or just do a quick search here for generic ports that will probably work fine. Perhaps you could also test the accounts by setting them up in a softphone running on a PC on the same network - if that works then it proves there is no problem with passwords or access to the accounts.

Second part of your question, answers can be found in the Voipbuster forum there is a list there of the sip address format for all the betamax group. Its probably going to be something like sip.username @ voipbuster.com (obviously change 'username' to the name of the party you want to call)