My iphone 4s power button is stuck?

I don't think I have dropped it or anything, it's just randomly become stuck today and it doesn't matter how hard I push down on the power button it will not work. I've tried blowing compressed air onto it and seeing if anything is jammed in it but it seems ok… Who do I contact to get this fixed? Do I go to an apple store or do I go to Three since I have my contract with them.

I suggest visiting an apple store, since iphones is their area of expertise. The chaps at 3 specialise in all kinds of mobile phones, so may be [slightly] less experienced. In the meantime, go to settings,-general,- accessability, and turn on assistive touch. A small grey square with a white circle will appear. Tap device, and then you can use this menu to lock and unlock your iphone.
Really hope this helps.

Its an iphone… Hit it with a hammer!
Take it to the apple shop and they'll sort you out or if its the actual button thats broke it may be cheaper to fix it yourself if its out of warrenty!