I have 1 trunk with 3 DIDs; each DID has 4 channels. I use Freepbx 2.5.x in trixbox.
Often time, I found that the system can accept 2 simultaneous calls for one DID without problems. However, when the 3rd call arrived to same DID, my system did not ring extensions–the 3rd call was connected to the VOIP provider’s voice mail box.
I called my VOIP provider and they said my DID does have 4 channels. They said it is my system that did not take the 3rd calls on the same DID.
I looked at my freepbx setting. The maximum channels under “Trunk” was blank, which means that there is no limits on channels.
Great advice. I contacted my provider again. I was told that 4 channel per trunk (even I have 3 DIDs on that trunk). Because I have 2 channels guaranteed for one DID already, there are only 2 channel left for other 2 DIDs. That explain the reason. I had asked them to increase my channel for the trunk.