It is possible because the Storm is a global phone but the phone will have to be unlocked. Verizon would have done it for you while you were a customer. Now, you'll have to look around online to see how to unlock it.
Plug your phone into your computer, bring up iTunes and open the ringtone folder in your iTunes library. Drag and drop the ringtone into your phone icon. A ringtone folder should appear and the ringtone should be in it.