You should be able to /tell people things even if they are not in the same lobby/game as you. Getting a hold of people on your friends list would be much easier.
Yup, /tellfriend, if they aren't going to make a new friend system, make this command, otherwise u can't contact your friends if they don't have skype etc./tell can only be for everyone. This could be very bad for YouTubers who just want to play with out spam for everyone who can on the server. You could make a new command like /tellfriend which only relates to friends.