when you sync an iPhone with iTunes it performs a backup of the phone but it only keeps one revision back it’s not like Time Machine. if you do a Restore of your iPhone iTunes will create a second backup that is separate from the one/most recent normal sync backup. so typically after Restoring an iPhone you will have two backup options to restore from: the backup created immediately before initiating the restore and the last normal sync backup. you will not have a Time Machine-like option of going back to a specific date to restore from.

iTunes stores the iPhone backups at ~/Library/App Support/MobileSync/Backup in 10.5 Leopard possibly elsewhere (but probably similar path) in other system versions. the backup is stored as a folder identified by a long string of characters this string is unique to each iPhone. if you want to restore an iPhone from an older backup you can replace the backup folder that is currently on the computer with an older backup folder pulled from Time Machine. after replacing the backup folder re-launch iTunes and Restore the iPhone from backup. you should see two backup options to restore from when you select a backup option iTunes will show you the date of the iPhone backup. select the appropriate backup date and restore the iPhone.