If you have the manual, check section 105. Basically, you create a dummy extension that is 'call forward always' using a system abbreviated number. Then anything sent to that extension via C/F or direct transfer will go to the phone number. IF the extension is allowed to C/F, AND unsupervised trunk to trunk connection is allowed.

When I was young, I was Liberal. As I aged and wised up, I became Conservative. Now that I'm old, I have settled on Curmudgeon.