How to know whether this iphone4s is unlocked or not?

I got sold an iphone but I'm not 100% sure if it's locked or not. The thing is that I want to sell it on ebay. I have a microsim but it is not activated (I'd need to top it up in order to activate it and I don't want to pay £10 in vain). My current phone takes a normal sim so I couldn't use that on the iphone to check.

If it's unlocked, I can sell it for more on ebay so how can I check whether it is or not?

Try going to SETTINGS then ABOUT then second from the top says NETWORK, see what it says on there, hope this helps

Hold down hash, if the phone goes onto silent then it is unlocked

1) ÔvÔ, your weird.
2)Restore in iTunes and see if you get the "Contgratulations" message