I use an older computer that doesn't do syncing with new gadgets so I can't check but it would surprise me if there wasn't some way to turn off wireless syncing. Check:
How to Use Wireless Sync in iOS 5 - http://www.pcworld.com/article/242242/how_to_use_wireless_sync_in_ios_5.html
iTunes 10.5 and later: Troubleshooting iTunes Wi-Fi Syncing - http://support.apple.com/kb/TS4062
Limnos, all I can say is that I'm surprised there isn't anything more obvious. Maybe I'm missing something, but if I try to work from the iTunes side, iTunes will never actually recognize the iPhone - I just get the message saying to load iTunes 10.7. Since it won't load the iPhone, I can't get to the screen where I could turn off wifi syncing for the phone. If I try to work from the iPhone side, I can't find a screen where I can specify that I want it to sync to the notebook, but not to the iMac.