The restrictions are lifted off and on and your friends can register in the times they lift it. Mainly, they don't want to congest the starting areas so that it becomes unplayable, so none of the restrictions are permanent. If you have the patience, you and your friends will be able to get on the same server to play together eventually.

If you and your friends somehow started on separate servers, server transfers will be implemented for new players 2-3 weeks after launch. Whether that transfer is free or at a cost is unknown.