what are the possiblities to do for configuring ring time or number of the ring before redirect the caller to the unity?
thanks in advance
Here is the way to change this, "System Wide" :)
Go to Cisco CallManager System Parameters from the Cisco CallManager Administration page. Select Service > Service Parameters.
Select the server to be your IP address and the service to be Cisco CallManager from the drop-down list.
Select Forward No Answer Timer (sec) from the list.
In the Value field, insert the timeout that you would like to configure (the time must be inserted in seconds). The default is 12 seconds.
Click Update on the top of the page.
Note: You do not need to restart the Cisco CallManager service to implement the changes.
From this good doc;
This can also be changed on a per Device basis on the Phone configuration page via No Answer Ring Duration = x number of seconds.
Hope this helps!