We have an interesting scenario where we seem to not be able to transfer a call.
Config
1 POTs line ( in use)
SIP trunk from Packet 8
If an additional call comes in (the pots line is busy), it rolls to the packet 8 service. Our receptionist picks up talks to caller, places them on hold. Receptionist verifies with the person being called if they wish to speak with the caller right now. Receptionist then tries and is successful at getting the call back off hold, however she can never transfer the call, we end up calling back the caller.
This process seems to work fine until we have more than 1 calls in progress.