Funny you should ask. Just right now I was reading up on requirements for cellular devices (including phones) that connect to networks in the US. In addition to the FCC, US carriers themselves also have certification requirements, which are different for each carrier. These cover things like transmission and reception power, pattern and sensitivity as well as regulating unintentional radiation within and outside of the allocated spectrum. Some carriers perform these certifications themselves and some require manufacturers to work with 3rd party testing labs.