Unfortunately Active Phone does not work with TM751 as it does not send rf commands through the palmpad html.
The main (underlying) problem is that the "image?Act=getmodules" command through http does not return the device type. Therefore it is not possible to know whether it is an RF or a PL receiver. Even though one could send an rf command through the http api, the palmpad html only sends plc commands, not rf.
(I realize the TM751 is not a good option when combined with the CM15A as it cannot receive plc and does not know whether another device already transmitted the rf command through plc. So it might end up messing up the signal by resending it. I decided to replace them with rr501's because they have plc receivers, are compatible with other transceivers on the same housecode and they would work with Active phone)