Can I sell my iphone 4S when it is still on contract?

As you all know the iphone 5 is coming out soon so i want to sell my 4S to get the 5 but I still have 6 months on my contract so I want to sell it on eBay many thanks Louis

Yes you can.
But you are still legally obligated to pay until the completion of your contract.

You can sell it and buy the new phone. You will probably have to add 2 more years to your agreement

Strictly speaking no. You do not own the phone. Read your contract. As long as you keep on paying your contract charges then the network is very unlikely to ask for it back so you could in theoryt sell it but remember it is not yours to sell.

You can, but the 4s is only worth $250 tops.

The phone is yours (the phone company never want it back)
but you will still have to finish paying for it.

That said,
if you only have 6 months left, they may let you do an early upgrade,
wait 3 months and you will be eligible for early upgrade anyway
- and maybe the ip 5 will be cheaper anyway, after the initial rush to get one.

3 months, not so long to wait (esp as lots of pre-orders will take time to get through)
Oh, and everyone will be selling ip 4S's so the price will drop through the floor?