you could also simply send them private messages. once you've started
exchanging messages, you can add each other on skype and take it from
there. at least, this has been my experience on this website.
italki does offer its users the option to block private messages until they've accepted your friend request. in this case, you'd need to add the person as a friend to be able to contact them.
I don't know about any such limitations.
good luck and have fun!