Problem with syncing 2 iphones to the same account

Question

I have 2 iphones -a 3gs and a 4g, each started out with thesame contact info. Eventually each phone had a slightly different set ofcontact info.  I named each phonewith a different name on iTunes.  Itried to sync them to the same itunes account thinking that each phone willupdate by computers address book and this way I would have a mirror imageaddress book on both phones and the computer.  The first time around it created duplicate files, in otherwords instead of updating a certain contact with possibly a new phone number,it created a new file for that contact with the new phone number and kept theold file with the old phone number. I cleaned up contacts on one of the iphones and then reset the addressbook with an older back up and then did the sync again, but this time for somereason instead of updating the computers address book with the clean versionthat was on the iphone, the reverse occurred and my old back up copy of theaddress book was entirely copied over the iphone contact list.  So now I have lost all the updates thatwere on the iphone.
I have 2 questions:
1. Is it possible to restore the lost contact list from theiphone or is it lost forever?
2. What did I do wrong in the syncing process that causedthe computer's back up copy of the address book overwrite the new and updatedcontact list on the iphone?

Answer 1

The best way to do this is to create two separate computer logins. That way, you have separate address books, separate itunes accounts, separate everything with no chance that each other's data will become intermingled.