Backup Assistant question

Been using BA for quite a while now and am really happy with it.


My active, newer phone, is obviously synchronized with BA's online database
of contacts. It "checks in" every day. It contains about 400 contacts.

I'd like to activate an older phone I own, on which I previously used BA.
That phone has about 200 contacts in it.

When I activate the old phone, what happens to the contact list in that
phone? Does BA "wipe" it, and replace it with the current list?
What if I have an invalid, older phone number for, say, "John Smith", in the
old phone, and "John"'s new number is in the database? Does it wipe out the
entire listing in the old phone, and replace it with the "John Smith"
listing in the database?

Sorry, I guess this is confusing, but I'd like to know if re-activating my
old phone will cause me to lose any old listings I may have had in it.

Someone out there knows.

Thank you in advance, "someone".