Hi. I've just tried using the built in video calling feature and couldn't get it to work. I was calling an iPhone and my screen showed that the other phone was being called but the recipitant's phone did not ring. I then called them with a normal voice call and it worked fine. Is this a known problem and is there a fix? I know I can use Skype or another third party app but I'd rather use the built in features if possible. Thanks.