Traditional three-pin telemark bindings are common amongst telemark skiers that favor the backcountry. Sole extensions are used to attach the telemark boots to the bindings. Three holes in these extensions are designed to match the three vertical pins in the bindings. Three-pin bindings are suitable for short backcountry tours that do not involve extensive downhill skiing. If you prefer longer tours with more downhill skiing, you might be better off choosing a three pin binding that comes with a heel cable.
Backcountry skiers should look for bindings that come with a brake. These are crucial in the event of a fall. They keep the skis from flying away from you. If you plan to do a good deal of uphill hiking, choose a lightweight binding. Also, choose bindings that can be adjusted by your ski poles. That way, you won't have to step out of your bindings when you transition from apline to touring mode, or vice versa.