Last week, I’ve ran into an issue with VOIP busy signal. After troubleshooting, I’ve realized that the system has run out of voip channel resource. The system was configure for 8 sip trunks and 10 voip phones. We had configure this system with the SL2100 Main Chassis / CPU combo package (0x0x0). By default, it comes with 8 VOIP channels. Each VOIP phone uses a channel and each sip trunk uses a channel. In short, if you needs 8 sip trunks, make sure you have double the amount of channels which is 16 voip channels allocated for the system.