Well, it depends on the configuration of the system.
Without fwd no answer coverage set, the phone will ring 4 times (12 seconds, 1 ring every 3 seconds roughly). This is a global setting under service parameters for call manager service you can set to lower/higher value then 12 seconds. The field under service parameters is Forward NoAnswer timer.
But in CCM 4.0 and higher, this is also configurable on each DN under the phone configuration. Under the phone DN config page, under the forward no answer setting will be another field for number of rings (or seconds).
You can also configure a coverage extension, so if the fwd no answer timer expires the call gets forwarded to another device/phone/DN or VM, etc.
The more a call gets forwarded around waiting to be answered, the more rings the caller will hear possibly.
