World of Warcraft is home to over 11 million players. With more servers than I'm going to bother to count, friends can be pretty spread out. Perhaps friends enjoy different rulesets or started the game without knowing about their closet WoW friend. Maybe a gamer has made a friend using the current Looking For Dungeon tool and wouldn't mind doing a few more dungeons with their new buddy. Whatever the case may be, Blizzard believes there is demand for a way to invite a player from another server to do a dungeon with you.
A cross-realm dungeon feature is in the works and it will let you do just that. A player from Server A, for example, will be able to use their Real ID connections to send out a party invite to their friend on Server B. From there, the group from different servers can use the LFD tool to queue for dungeons or heroics. However, that ability will cost you. Only the player doing the inviting will need to pay for the service, but there will be a fee to use this feature. Gamers can probably expect a monthly fee for the service akin to the World of Warcraft Remote feature (an extra $2.99 per month).
There's no estimated time of arrival for this feature. There's also no word on how much this feature will cost. One thing is certain; however, some players aren't exactly pleased with the premium part of the announcement (of course, some don't care). I don't think either stance will greatly impact Blizzard, though.