When I pull the cover off my cellphone there's a little FCC ID on it, as there is for most electronic devices. However, with cellphones you can actually get a whole wealth of technical info about it from that ID. Just type it in here:

http://www.fcc.gov/oet/ea/fccid/

Example ID:BCGA1203

Grantee code is the first 3 characters, and the Product Code is the rest.
The first page that comes up breaks down the data per band. Most of the technical information is in the "Test Report" links. It will give you power output, EIRP calculations, power curves, antenna gain and much, much more.

Thanks to KE7HQY for this information.