I would imagine that the way to match the voltages/frequencies would be to convert to DC, at an agreed voltage of course ?? I am not an electrical engineer.
As an aside I live in the Docklands area. There are iron covers beside the quays which are marked GPO, these are little hatches which would lift up to uncover a telephone socket for the ship whilst it was berthed.
In that area we suffer from the telephone infrastructure dating from that era, even though there are hundreds of new apartments in the area. ADSL broadband is dire in that area. One of the reasons I was told is tthat the telephone lines were originally used as alarm lines for the dock warehouses.
To prevent Mr Big and his team of robbers splicing into the lines and short circuiting the alarm, the lines had to go direct to the exchange without junction boxes. The exchange being in Bermondsey about 2 kilometres away. I used to get modem level ADSL speeds in my flat, which simply conked out on a hot day.
Thankfully now have a superb fibre optic connection via Hyperoptic, which brings fibre to the building then fans out via Cat5 cables to every apartment.