iphone 3g black faulty -

IPHONE 3G 8GB BLACK WITH CHARGER NO BOX SLIGHT FAULT IS THAT U CANT MAKE CALLS OR TEXTS BUT INTERNET WORKS SO LIKE A IPOD TOUCH WITH 3G INTERNET CAPABILITY EVERYTHING ELSE WORKS FINE SO PHONE SHOWS IT FINDS SIGNAL JUST SAYS CALLED FAILED SO COULD BE EASY FIX PLEASE NOTE ON NO OCCASION DOES IT SAY NO SIGNAL ETC NO SERVICE ETC ETC CHEAP ONLY GETTING RID AS GETTING 4S THANK YOU