Here is the scenario. The main office phone is an AT&T landline, which if busy, is configured to dial a sip line, call it XXX-XXX-XXXX <sip 1 number>. This works just fine, as long as the XXX-XXX-XXXX <sip 1 number> is not busy. XXX-XXX-XXXX <sip 1 number> is set to forward to YYY-YYY-YYYY <sip 2 number> if SIP1 is busy, but this never works. The AT&T line never makes it to SIP2, if SIP1 is busy.
Any idea how to fix that, or a better work-around to accomplish the jist of the idea.?