I was thinking it would work like the IsByondMember() proc:
is_guest = TRUE
src << "Log into your pager for a fuller game experience!"
is_guest = FALSE
src << "Thank you for playing!"
I have a habit of blocking guest keys and from what I know of, there isn't a legit way of checking if the player is on a guest key or not. This would be a nice simple addition, in my opinion.