IP Softphone and Digital extension the same

[Telecomboy]

I am trying to set-up a scenerio where a customer can utilize the same extension for their IP Softphone (when working from home)and their Digital 4412D+ (when they are in the office). I tried setting up the extension as a "hotdesk", but that wouldn't work for the IP Softphone. When I was logged-off of the digital phone, I tried logging in to the IP Phone with the extension and the password created under login of that user's telephony tab. It keeps coming back with the message that it cannot log-in due to either password or extension being incorrect. If the 4412D+ is left logged in, it will let me log into the IP Softphone, but when making/taking calls it works through the 4412D+ instead of the IP Softphone. Any ideas would be appreciated.