Hi Del
Don't know about restoring the default message - you may have to look at the asterisk pages on voip-info. It's not really an area I know well, 'cos it tends to just work. I suspect you can just manually delete your recording but I'm not sure (I don't have a machine here so I can't check).
Aliases can point to any number (or range of numbers) internal, external, mobile, even other aliases (2.1.14), just type the number in and nominate a trunk for the alias to use. Have a look at aliasing in the docs.
Kind Regards
Selintra