The laws vary from state to state. Most states require you to register as a Money Services Business and to comply with their regulations. The federal government also requires you to register as an MSB and to register in the states you do business in (to the extent that they require it).
IANAL
Do I need MSB from every state if I conduct business in one state and sell bitcoins to people in other states?
For example, let's say I have my business in New Jersey and I sell bitcoins to people in New York or Texas or Florida, do I need a MSB for every state I sell in?