Can i use my contract sim in iphone 4s?

I'm wanting to get the iPhone 4s however, on my current contract with my htc hd7 my upgrade date is only available in march and i don't want to wait any longer as i really dislike this phone. If i got the iPhone 4s could i just use my contract sim in it (obviously changing it over to a micro-sim first) I was considering cancelling my current contract and starting up a new one however i didn't want to pay the £153 termination fee. Would i still get my contract use-age in the iphone, like my unlimited texts and my 1gb of free data?
Any information is very helpful as I'm not too sure about these kind of things.
Thank-you.

You need to ask to change your simcard to a micro sim to use in the iphone

Of course your contract sim will work in a iphone 4s. A contract isn't about the phone, its about what you get a month.