This is an interesting article on this subject:
http://www.cbsnews.com/8301-501465_162-20008909-501465.html
Doesn't look like the FCC regulates where an antenna can be, they regulate how much radiation a body can absorb from a phone.
Companies used to get around this with pull-up or stub antennas but now they moved them to the bottom of phones to keep them further away from the body.
Apple moved their antennas to the sides of the phone, hence the problem with reception being more prevelant with the iPhone 4 when you wrap your hands around it as opposed to other phones where the antenna is harder to cover since its on the bottom.