I actually signed up with Amazon on Thursday for a Family Plan. Never asked me for deets on anyone other than myself. We were both new AT&T customers, but what I would do is if you need to get a NEW customer discount, just use the name of the person who isn't on AT&T.
Don't forget too that the Caller ID thing only applies to landlines and some corporate lines, as on cell phones they don't pull TRUE Caller ID info. If it is an issue just call CS and ask them to add someone to the account to authorize changes and then ask them to change the Caller ID on the specific line you want to change to that user (if applicable).
'It's rich drunk, it's kinda like business drunk. Either way it's legal to drive' - Jack Donaghy