iphone 3g locked after updating to 4.0.2 in india

hey guys can u help me out... my brother presented me an iphone 3g this year.. he bought it from us.. but recently i updated my iphone to new software update... now its locked.. it showing me itunes symbol n usb cable pointing towards itunes symbol... its asking me insert the sim which i got with this mobile.. but unfortunately i lost that sim.. so how can i get my mobile back to normal..?? how can i unlock it?? i stay in mysore, karnataka...