The code to turn on call forwarding on a different DN would be #6012, and not #6011. If the PhDN is assigen an owned then you can use #6011 at the phone on the button setup as the PhDN.
I would probably put 8888 on a phone, assign an owner, and then user #6011. From testing I found that call forwarding seems to work better when the PhDN has an owner.
The phone display will always show CF-ALL External, but since you are migrating away from the Toshiba I don't think this will bother anyone.
I have user a Multiple Call group with the #6012 and had some good success with using #6012

For a PRI, you can call forward at the DID settings. For the DIDs use the destination of Dialing Digits and 915552222222. The number should be exactly like you would dial it from another phone, with a 1 if required in your area. A one is usually requires so that the PBX knows you are dialing a long distance number and not a 7 digit local, but that depends on your area and the PBX settings. Pickup a handset and dial the number if you are not sure.

If the calls fail to forwardwhen testing, then it may be the Class of service doesn't allow tandem CO connections. A second possibility is that the PRI carrier isn't allowing foreign DIDs as outgoing caller ID

Good luck

David
Tele Express Business Systems