There are a number of ways to get a call originated from an IVR to a remote telephone number. The easiest is to create a dummy extension and then have the dummy extension set to call forward to the desired external number. The issue is that once answered, how to effect a transfer. You do not provide enough information such as who/what/how is the call being answered at the remote dialed number and, assuming for the moment that a human dialed the number, how the call would normally be transferred to your ultimate destination/extension.