I did install FreePBX on a VM-Ware and did configure trunks and extentions. A firewall does forward ports 5060,5061 and 10000-20000. FreePBX System-Status shows the correct numbers of online IP-Phones.
Now, an external does does arrive at the extention (rings and dispays the caller-number). After lift off - the caller cannot hear me and I do not hear him. When I hang-up, the line to cutted.
What could that be?