From where to buy a sim card with a usa number? (traveler asking)?

I'm from Europe.
I will go to usa (ny and LA) in December.
As i will go there for business i want to buy an american number. But i want to have it before i live because i want to give it to people who want me for work so they can call me.
From where online can i buy a sim card with an american number?
I have an iphone 4s and i want a sim card that it will have for example 3$ . I don't want to use the sim card in order to call. I want to use it so people in america can call me.
What can i do? Fromwhere can i buy it?

Well you wouldn't be able to get the SIM before you arrive in the US, unless you have a contact there that can receive the SIM & ship it to you, but since you are going there anyway, that makes no sense.

"i want a sim card that it will have for example 3$ . I don't want to use the sim card in order to call. I want to use it so people in america can call me." This also makes no sense. The SIM is what allows you to make and receive calls, so it would have to be used either way.

As far as getting it you would have to go to a carrier & get it from them, of course a GSM carrier in which case would be either AT&T or T-Mobile. Also the phone would have to be unlocked in order for any of those SIMs to work in it.

You need to get one from one of the American providers that support iPhone 4.

What you could do is get a Google Voice number now, and forward to the number you get when you get an American iPhone SIM.