A BT Micro is a box including Broadband router, WLAN, & a DECT cordless handset, all in one box. It's been discontinued by BT.
https://www.businessdirect.bt.com/pr...4869-434K.html
If the old phones work on a direct exchange line but not the Pana 206, it needs master sockets or rewire the phones to use internal ringing capacitors. The centre pair of the Panasonic RJ12 connectors connects to 2 and 5 of a British Telecom connector.
If the phones don't work on a direct exchange line, then they need to be rewired internally.
Wiring guides for almost everything is here
http://www.britishtelephones.com/pstconv1.htm
Not sure if the Pana 206 will do it, but the larger systems can have hotline dialling set up so on lifting the handset the system will automatically dial to an 'operator' extension allowing even dial-less phones to be used.
(I had exactly the opposite problem with a Norstar system some years ago, which requires extension sockets with the wires to 3 and 4)