If you're in the USA, you might wanna take a look at this:
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Also, dependant on your state (if in USA) other licenses might be required to register your business. Mostly the EIN is needed to purchase / sell / setup bank accounts for your company. There's different types of corporations.
Also take a look at :
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and
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As for whether or not all need it, no some do not need it. But be warned that if you don't have one, there's the likelyhood that you also don't have the proper licenses to resell and may get in trouble when tax time comes around. It's always better to make sure everything is legit.