I have a problem with my UC540 with it hanging onto an incoming call despite the fact that the calling party has terminated the call.

I would call my trunk line from my cell and the autoattendant will answer.  If I hang up my cell, and then try back the same trunk immediately, I get a busy signal.  I would then have to wait 4mins before I can call the line again.

I tested this with an extension (IP Phone) as well.  I called the line and punched in the digits to get to my own extension then hung up on my cell. What I realized is that the extension kept on ringing despite the call being terminated. I would get then get the email notification 4mins after the call terminated indicating a voice mail.  The majority of the voice mail message would be a busy signal tone.  If I answered the call on the extension this problem would not happen.

I also have a trunk line used for fax.  This does not use the auto attendant, but transfers directly to one of my FXS ports.  Strange thing is I don't get the problem with this line.  To test, I configured the "fax" line to use the auto attendant in the Dial Plan->Incoming settings and I got the same problem described above.

The incoming call lines and the fax line are from different providers.

Has anyone experienced this problem? If so, how did you resolve?

Thanks,

Tarquin.