that is four years old...
http://en.wikipedia.org/wiki/Comparison_of_instant_messaging_clients
go to the bottom chart and check the Message Logging column...I dont know what software the kids used, but a lot of younger people use Trillian so they can chat with people using Aol, Yahoo, iChat, MSN on one program
the clients can log, that's for sure. but the issue is - do the providers log all the sessions?