This issue can occur when the maximum number of calls on the line has been reached or the user receives the Maximum Number of Calls and Busy Trigger on the line settings of the phone.
You can configure a maximum of 200 calls for a line on a device. The limiting factor is the total number of calls that are configured on the device. As you configure the number of calls for one line, the calls that are available for another line decrease. The default specifies four. If the phone does not allow multiple calls for each line, the default specifies two.
The busy trigger, which works in conjunction with Maximum Number of Calls and Call Forward Busy, determines the maximum number of calls to be presented at the line. If the maximum number of calls is set for 50, and the busy trigger is set to 40, then incoming call 41 is rejected with a busy cause (and is forwarded if Call Forward Busy is set). If this line is shared, all the lines must be busy before incoming calls are rejected.
To resolve this issue, increase the number of calls per line, or try a different line.
For a workaround, perform these steps:
- On the Cisco CallManager Admin page, choose Device > Phone > Maximum Number of Calls or Busy Trigger. Reconfigure the phone with the issue.
- Increase the value of Maximum Number of Calls and Busy Trigger on the IP phone line configuration according to the number of shared lines (or the number of calls coming on the same line).
For example, you can set the busy trigger to 5 on 7960 since there are six lines, and one line can be kept free for a conference or outbound call when all other lines are busy.
For more information, refer to How Multiple Calls Per Line Work in Cisco CallManager 4.0.
This issue is documented Cisco bug ID CSCee24036 .