simple question

Hi My name is Mohsen Asghari, master student in Computer EngineeringI have to create a communication center based on GSM with OpenBTS,everything is OK, I have tested osmocom-bb with SMS in vty and it was perfectbut there is call problem. in both of real and virtual network this problem is bothering me finishing my thesiscan you help me understand whats wrong with my packages and installation? it is five months that I am trying to fix this problem but I cant.in the cm-service command I have a channel release from ms which the comments shows that the problem is about there is no free socket for voice....! _____________ yours sincerely, Mohsen Asghari