In regards to iTunes content, an iPhone can be synced with an iTunes library on a single computer only, and photos can be transferred to an iPhone from a single computer. When syncing an iPhone with an iTunes library on a different computer and the same for transferring photos to an iPhone from a different computer, all iTunes content and photos transferred to an iPhone from a different computer will be erased first.
You can sync contact info, calendar events, and bookmarks with the supported applications on multiple computers.
Your iPhone's backup includes data such as most iPhone settings, email account settings, contact info, SMS messages, notes, recent calls, call favorites, photos in your iPhone's Camera Roll, and 3rd party app settings and data created and stored by a 3rd party app. Your iPhone's backup is not a complete backup of all data available on your iPhone.
You can create a backup for your iPhone with iTunes on any computer. With your iPhone connected and without syncing, control-click on the name of your iPhone in the iTunes source list and from the menu window that appears, select Back Up.