I treat teleport the same as dimension door: once the spell transports you, you can't do anything else until your next action. Like most of the other solutions, this means that even if the attackers gain surprise, they don't get to take any actions during the surprise round.
Also, as a house rule, I allow a Spellcraft check (DC 25) to perceive an incoming teleport. Success doesn't tell what exactly is coming through, only its map location and approximate size (in Medium-size-creature increments). With a decent initiative check, it's possible for a prepared party to get the drop on the attackers.
Also, as a house rule, I allow a Spellcraft check (DC 25) to perceive an incoming teleport. Success doesn't tell what exactly is coming through, only its map location and approximate size (in Medium-size-creature increments). With a decent initiative check, it's possible for a prepared party to get the drop on the attackers.