I think it should be possible for the high level mages to teleport on the main island. Level 35+ mages should be able to transport anywhere on the main island and for going to foreign islands you would need to be level's 40 +.
Mental levels could affect this skill so that someone with a level 60 magic and a level 26 mental would fumble the spell constantly and lose all their mana. A level 60 magic with a level 107 mental would rarely fumble a spell though.
You would type /cast Teleportation <here you would type the name of the marker than you wish to teleport to>
There would need to be a new marker Colour that you can use once you have the teleportation spell. And that marker would be restricted to people with the spell. That way you can set the exact spot. And it would alert you if the area your teleporting to is unavaliable or restricted, e.g. inside kingdom castle walls