I don't have the manual here but OBT, as usual, is correct. The dil 1:1 does not exist in the US KXTA824 as I remember.
The door opener goes to an answer group as an option. You can try call forwarding but HOW ? will you operate the functions? To cwfd opm you have to dil a trunk...the door opener isn't a trunk.
Good idea, but I don't think it will work.
Your other question, DISA is inbound only to access system features...not out bound. Sorry.
