Sony Ericsson Xperia Arc and the iPhone 4. The StuckBuddy can also be used on any other flat surfaces like a mirror where you can then hang light stuff like keys.
Update: Mobilefun are running a promotion on the StuckBuddy. If you buy anything on the site, you will get a free Stuckbuddy simply by entering the word BUDDY in the rebate code section at the checkout. The offer will continue whilst stocks last.