O/T iphone help

Had a iphone on '3' which was unlocked but then reverted back.to locked, just put brand.new '3' simcard in but when tryin to activate the phone its saying that there is no simcard in the phone so it cannot.activate... Anyone got any ideas on how i can fix this? Does it need to be unlocked again to.work etc?

Thanks in advance

It is jailbreak unlocked or officially unlocked by your service provider?

Dodge guy in the market Caerphilly... Guessing that's jail break? .. He said not to update or restore it as that would relock the phone but that it would.just revert back to the original set up which would be '3'