I have both a SP504g and a SPA502G on 7.4.4 Firmware which generate an odd ringing sound when making a call to a local extension on my asterisk server. However, when calling an external number through the same PBX, the ring sounds normal.
The ring tone I hear on the calling phone sounds like the dialtone being played with inturruption of the ring tone or put another way, there is a background drone of dial tone while the ring tone plays over the top.
If I SIP trace the extension call and compare it to the external call, I see the Internal call sends back a 'SIP/2.0 180 Ringing ' message while the external call uses a 'SIP/2.0 183 Session Progress' response. Is this a bug in the firmware?