I have just bought a global sim card from Travel talk. After putting in the sim card it asks for a pin which i put in then seems to be all set. Says UK profile for the sim card name. Then when i made a test call to my old mobile then screen goes black/blank when the call is connected and stays like that after call is finished. I push the button on the phone to bring the phone to life but it doesn't do anything. It vibrates when i use the only other button on it which is to turn it on silent. Help! Is there anyway around this?