I accidently bought 10 of the 5200 series power cubes (even though the 7200 IP kit comes with 5 - 5200 and 5 - 3100 series). The 5200 power cubes will work on the 3100 series phones; I believe the difference is the 3100 series have a 90 degree connector on the phone end, but if you push the cable just inside the stand, it works fine and is not bent on the 5200 phone.