If that's all you want iCloud should do it perfectly. You can sync your contacts with iCloud and enable iCloud Backup to backup your photo roll and any documents you may have on the phone (much like an iTunes backup). And if you decide to switch from the iPhone you can still get them off of iCloud.com and export them as vCards which I believe most services should be able to import.
I use iCloud to sync contacts, calendars, notes, documents etc between my iPhone, iPad, and MacBook, and haven't had any duplication issues except for a few odd ones involving Notes where changes were made to a particular note before it had received changes made on another device.
This Apple page should walk you through everything you need:
http://www.apple.com/icloud/setup/