When configuring dual line on an ephone, this causes incoming calls to register as beeps while you are on call. This causes problems as the customer at the other end of the phone cannot clearly hear you.
There is a solution. You need dual-line to be able to transfer calls. What you need to do is stop the second call and make it go to voice mail. This is done by doing the following:
ephone-dn xx dual-line
The no huntstop command allows calls to continue to hunt to other ephone-dns if this one is busy or does not answer. The huntstop channel command disables call hunting to the second channel of this ephone-dn if the first channel is busy or does not answer.
Hope this helps.