Hi Robert,
Boob's Law - see footnote [1] on my previous post.
Field Telephones for WW2 Commonwealth forces would be the D Mk.V for front line forces, Telephone Set 'L' for Linemen, and Telephone Set 'F' for higher formations (basically an office telephone for people with desks). All of those ran on 3 volts from a pair of 'X' or 'S' cells. Switchboards for higher formations would be the Switchboard F&F (Field & Fixed)which could support 20 to 60 lines and could operate with three switchboards in parallel as a combined unit.
Switchboard UC "Universal Call" supported buzzer and magneto signalling.
Switchboard F&F is magneto only.
Telephone set D Mk.V was buzzer call but buzzer or magneto ring
Telephone set 'F' was originally buzzer and magneto signalling but the buzzer was replaced by an induction coil (microphone transformer) later on (for better audio quality) and became magneto only.
Telephone set L was magneto signalling (only).
(There may have been some earlier (Post Office 110) telephones still used by linemen, but the 'L' was rather better.)
(Plus the various Remote Control Units (Canadian) and the British 'E' could connect to switchboards as magneto telephones, of course.)
All the manuals are available from the WS19 website - I think I scanned most of them.
Best regards,
Chris.