your JAA RT rating, will get you your USA licence
go on a search engine, and look for restricted use Radio operators licences, by FCC.
Or read post no 2, and use this link.
They provide forms, and all data needed to issue a FCC licence based on your JAA RT licence.
Small fee, and all done.
You need one for operation of an N reg aircraft outside the USA. and especially if you are applying for RVSM or similar ratings.
OK?