[Asterisk-Users] Cisco 79xx and SIP 7.5 Problems

[C F]

I recently updated my phones Cisco 7960 phones (3 of them) in a high
volume call place, where the Secretaries use the 7960 phones to answer
inbound calls, as many as 15 simultaneous calls between all three of
them.
Since then I have had only constant problems, mainly that after 3
calls on a phone, if they try to xfer or do any ohter things
(sometimes just answer the 4th call) the phone freezes, they have had
this happen to them throughout the week. Until yesterday I decided it
must be a frimware problem, so I downgraded them to 7.1. Since then
(around 5PM EST yesteday) it didn't happen *yet*. So I'm assuming it
has to do with the firmware.
So my question is, is anybody else using 7.5 firmware?
If yes, do you have all the line buttons configured to the same SIP account?
If yes, do you see the same problem?

I also noticed that with 7.5 firmware callwaiting has to be enabled
for the second call to be able to come in, otherwise the phone returns
a Busy here, while with the older versions it could have been disabled
and it worked fine, the phone only returned busy here on the 7th call.
So I had to enable call waiting, the way I did it was that in the
SIP<mac>.cfg file I added
call_waiting: 3
I'm not sure if this is related or not, but that was the only change I
had to do to the config files.