Is it possible to have 2 phone numbers with one iphone 4s?

I'm opening a small business and want a separate phone number, but I want it to come to my iphone. Is this possible. I know I can always do call forwarding from another number but that's just too much hassle with having to get another phone and another plan or whatever.

Nope. Not possible.

There's the hard(ware) way:
opening your iPhone and then changing the simcard would be the unhandy but less complicated way.
there's the software way:
Use a Skype-account (or other such service) for calling! The negative point of this one is that on a normal phone the calling number looks like an error (but still full-functional).
you can also use some kind of old phone for business, and keep the iphone as personal one (or the other way round)
or you could sell the iphone and buy a dual Sim android smartphone with bigger screen, free apps, and smaller price tag as well as a bigger camera.

Of course not, not without paying 2 bills. 2 sim cards sounds like an idea, but each sim card needs a phone plan separately to use it.