I haven't talked with anyone about this, but my answer would be NO, it's not okay. They might start to have too much in common with "worldly" folks and something other than religion to talk about. I guess they could do it amongst themselves, but I could see this opening up a conversation with a worldly person who sees them send texts and making phone calls to their witness friends. Then a conversation between the two individual (JW & Worldly) would start. Next thing you know they are bonding and....BAD association spoils useful habits.
When it came to sports in general I remember them saying to be careful with being to involve in them. I don't remember any young witness boys getting together to play football or basket ball on regular basis The few times I did recall, it didn't seem to last long.