So my boss has a husband/wife iphones. He synced his with his Macbook and she with hers

He let one child use his MCB on a trip. How does he sync his phone on her MCB.. It thinks it is her iphone.

Wow, what a confusing question

So if I can interpret this, sounds like somebody you know wants to sync their iPhone to a second computer?

Here's how iPhone syncing works:

There are 3 categories of syncing:
Data (contacts, notes, bookmarks, etc.)
Media (music, movies, podcasts, ringtones, etc.)
Apps

Any one of these categories can be sync'd to one computer at a time.

For example, I sync Data and Apps to my MacBook Pro and Media to my iMac.

However, if I decided to sync Media to my MacBook Pro or some other computer, the Media that is currently on my iPhone would be replaced by the Media I choose on from the MBP.

To complicate matters even more, Media can also be managed manually. This will allow you to put music (or other media) on from more than one computer at a time.

Also Data such as Contacts, Bookmarks, Calendars, etc. can be sync'd via MobileMe AND/OR a computer (as long as the iPhone is running OS 3.0 or higher).

Hope that helps.

yes it was a confusing question when put to me..
2 iphones in a family , both have their separate contacts and emails. there were 2 separate MCBs to sync individually,,now only one. Both want to update their iphones but are afraid of losing data . Don't know if they have mobile me.

Yes, two iPhones can sync to the same computer. I would recommend setting up two users and each iPhone sync to each user. Otherwise they would have the same data on each (unless that's what they want.)