Do you have to wait after you dial the last digit of the extension? If so, then you have an overlapping dial plan. The phones are waiting because they are waiting on you to enter more digits.
If your Cisco phones have extensions like 7215 for example and you have a route/translation pattern like 72XXX. Then the phones will wait for the inter digit timeout before putting the call through.
Try entering the Cisco phone extension then press the # key. Does the call go through immediately?
