Well since you're in the "world" no one can answer that for you. The laws will vary depending what country in the world you are in. You are being too nationalocentric with your question. But, if you're in the US, unlicensed transmitters are covered under Part 15. Here is a link that answers your question. Incidentally in the US it is illegal to build a transmitter and then sell that transmitter unless you have had it tested and you are licensed to build transmitters. That seems to be a very touchy thing for the FCC right now and they have fined several EBAYers for selling a few homebuilt transmitters under part 15.