I believe your problem may be due to the wiring configuration between RJ-11 and BT Plug. The RJ-11 plug relies on all signalling to be done on the middle two wires,where as BY require the outer two wires with the third being the ring capacitor circuit. This is probably why you are getting no signal. It is the same problem if you use either the AX520 or the newer AX522,both use RJ-11 sockets and connecting direct to a BT phone will result in no tone. You need to use a RJ-11 to BT Crossover Adaptor, just like the one below:-

You can get these for most electrical shops etc.

Regards