What happens if I connected my phone to my laptop to update the software and now I want to use my phone on my desktop computer? There are no songs on my phone and the photos are backed up. Can I erase everything and sync it with the new computer or will I lose all my contacts settings ect.? Also it is unlocked so I assume I will lose that if I erase and sync?
P.S. I hate that Apple only allows one computer to be connected to a phone. I use my phone on both my laptop and old desktop.
If there are no songs on the iPhone and you have your photos backed-up, there is no bad in syncing your iPhone with your new iTunes. The contacts will not get erased. On the contrary, iTunes will automatically create a backup copy of your contacts, calendar and notes during sync (what is called an iOS backup).
The fact that iTunes is rather restrictive when it comes to syncing with multiple iDevices is known and unfortunately it is the way it is. You can try and go around this in the future by using third-party backup software for your iPhone. Here is an article describing some more popular such programs: