Lost contacts in iPhone

I was given an iPhone a month ago. I transferred my contacts from my old mobile phone into my Entourage Address Book and, with my other Entourage Address Book contacts (with e-mail addresses etc), sync-ed these onto my iPhone. All good.

A few days ago I noticed that the contacts from my old mobile had disappeared from my iPhone. I opened Address Book and Time Machine but nothing happened when I clicked on a backup before the loss of data (although Time Machine would go to earlier generations of the Mac HD). I then tried to get to the contact details in by restoring the data in Users/Library/Application Support/Address Book/Metadata. It appeared to restore all the files but none of the mobile contacts arrived in the Address Book. Finally, I copied the earlier Metadata file from the backup disk to the Desktop and tried to import the data into Entourage but this can only be done one file, eg one address, at a time and one cannot see what contact each file contains.

What has happened and how can I get the contacts from my mobile back on my iPhone (and prevent this from happening again)?

Thanks