sync antenna placement?

Hello, I'm looking forward to buying a signal booster for my phone. But I have no idea were the placement of the sync's antenna is. Show can somebody tell me or show me the area in which the antenna is?

The salesman told me it was in the back of the phone.
Cell Phone Accessories: Case,Pouch,Holster,Charger,Phone Tools,Headsets

The antenna is in the lower part of the phone, right below the battery.