Extensions like the 200, 202, 1022. Obitalk can link the phones to have an extension # like 20# to dial one device, 21# to dial another. IE if the 200 is 20 and the 202 is 21 and the 1022 is 22, I can dial or forward a call between the phones by using the two digit phone extension and #. Obitalk doesn't have the 2000 series listed to be able to assign an extension number to them. I can make extension 23 (in my case) but the Obi2062 Obi Number does not show up to add it to my linked devices. It would be very helpful if it did.