iphone 3g or 3gs not sure 8 gb on orange *

iphone 3gs/3g on orange 8gb black..... i bought this a few week ago and was told it was 3gs... however, came in a 3g box and im pretty sure it is 3g but not 100 percent. good condition and comes boxed..... only slight problem is that sometimes signal is hard to get. took to shop guy says phone antena may need replacing cost 7 pound but they have to send it off cant be bothered to mess about like this as IT DOES RECEIVE SIGNAL SO NOT BLOCKED just rather sell it does receive signal just every now and again it is either week or will search for a while. please text or at least text before ringing cheers.