The teleporter actually has two functions. First it summons a portal that only you can see. Right-clicking the portal gives you two options. One option is to port to a group member anywhere in the world. The second option is to summon a group member from anywhere in the world to your location. Once you use an option the portal goes away. I think the recast time on it is 60 minutes.
Yes, this works across zones and yes it works in dungeons. A player must meet the requirements for the zone before they can be summoned to you. So this means they have to have access to the zone and can't possess a lockout timer for another instance of that zone. Our goal with the summoning ability was to allow veterans to share the "coolness" of this item with other players that might not have it yet.
http://forums.station.sony.com/eq2/posts/list.m?topic_id=463788&post_id=5171689#5171689
Wow, This will make things a lot easier. On the PvP side it will be intresting to see how this effcts camping of zone ins.