The guesting feature has been announced to be released in the January content patch, due 28th Jan. Full post on the ArenaNet site at https://www.guildwars2.com/en/news/guesting-is-coming/.

With guesting, account transfers to other worlds will cost gems, so it’s important that if you have any friends that join the game you make sure that they’re aware of what server you’re on if they want to play WvW with you.

A summary of how guesting will work:

• At the character select screen, choose World Selection
• Select a world from the list, and choose “Guest”
• That world is now eligible to play on for the next 24 hours
• You can have up to 2 worlds that you are guesting on in any 24h period
• You cannot play WvW for a world you are guesting on – you get put back on your own world if you select WvW
• Guild influence/bonuses/upgrades are still tied to the world you’re currently playing on – i.e. if you’re guesting on a world that is not Jade Quarry, the influence is sent to the other world and you will not get the Jade Quarry guild benefits while you are over there. 🙁
• You can only guest on worlds in the same region (i.e. US worlds when you “live” on Jade Quarry).
• The cost in gems for transfer will depend on the population of the server. Given that Jade Quarry is one of the high-pop servers, it’ll be in the most expensive transfer category – making it more important for new friends to sign up to the right world at the start (if they want to be on the same world, that is 😉 ).
• Even with paid transfers, you will not be able to transfer to a “full” world. Likewise, transfers will still be restricted to once per week.