No, you don't have to go outside. If you go down the Towers elevator and get off on the right floor (one above the Towers lobby, IIRC) you can walk right into the Waldorf=Astoria lobby. It's hard to visualize completely until you've actually seen it but, as others have said here, it's basically two hotels in one building. There are two separate entrances and front desks but otherwise it's all within the same building. (I didn't "get it" until I'd seen it either.) Anyway, you won't have any trouble connecting with your friends.