Saying that, (after I bought the damn thing), I do have things working nicely with a TVA 4 port with NIC and 5 DECT cordless on extension 100 in the mix. Trial and error plundering my way through possibilities of the combo, but I have a nice setup now. My TVA custom service has evolved further and got everything accounted for for two busineses; time control custom service, day, night and lunch (we use when we are away) PBX control. Putting the system on night service but allowing callers to get through to an Inn suite has been bliss!! No more 3AM calls, we wouldn't have taken their booking anyway as it's usually a drunkard or some folks wanting a quick lay
Thanks to you, brokeda and all others for your help!