Pretty old thread, but worth to wake up.
T-43/TP and TA-312/TP has equal qualities in hence of plain telephony. In CB mode The phone acts as a regular telephone, no batteries needed, and the range of operation is about like a normal telephone, e.g. 14 miles on a twisted pair of common or field telephone wire. Putting in a pair of batteries, and using it in CBS mode extends the distance of clear voice transmission with several miles. (still connected to a regular telephone line)
In LB mode, it acts as a regular field telephone, point to point, or phone to a manual switchboard as SB22. Now the it may connect to telephones more than 20 miles away.
The thicker copper wires, and the more it is twisted the better. (within reasonable sizes).
If we look back in time, it was used fence wire, as the one and only wire, and ground as the other, this solution worked well for at least 10 miles in areas where it was no other electric current traveling trough the ground.
dsk