On Sun, 08 Mar 2015 21:41:27 +0000, Toby wrote:

The POTS side only needs ringing to drive proper bells (Bell 50c).

Would these work for you?
http://www.amazon.co.uk/RTX-WIRELESS...hone-White/dp/
B000NJQHL4/ref=sr_1_1?ie=UTF8&qid=1425850760&sr=8-1&
keywords=wireless+telephone+extension

http://tinyurl.com/pcugag9

Well that's the sort of thing and it even uses DECT but I don't think
you can pair the slave with anything other than an RTX master. The
pairing process appears to involve joining master/slave with a cable.

The ATA idea popped into my head 2 ms after pressing send but that
seems a bit overkill and involves wires. I was sort of wanting
something small and battery powered, there is quite a bit of space
inside a Bell 50c...

Butcher an old dect handset, switched 25 Hz oscilator, into 15:1 step
up transformer(*) to drive the bell?

(*) Small mains jobbie with 15 V secondary?

--
Cheers
Dave.