My personal "niche" was inspired by Fight Club, I did some research on US types and discovered whats what.
My first discovery was the 500 C/D, and I found a black one for peanuts on ebay US, black, no line cord, no handset cord, unfortunately the postage wasn't so peanuts to the UK.
Anyway found a site that does replacement modular line/handset cords, so I got a black RJ11 to BT PST line cord, new handset cord (10 foot) and it looked fine, even worked, but no ring!
Thanks to the folks on Singing Wires soon put me straight about that pesky wire aduster on the bells.
Next was the wallphone in the Paper Street house.
It was a 554 black tatty and with white paint splashes on it, and a smiley sticker.
Again stupidly I buy a beat up one from ebay US.
No line cord, grey flat handset cord and hard-wired!
So I had a spare black RJ11 to spades line cord, wired it up, then ordered a 5 foot and 15 foot spaded coiled cord from the US company as before.
Wired it up ( after researching how to open the thing without breaking the case) and with an RJ11 to BT socket again works fine.
I tried the 5 foot first, but have got bored with it and just changed tonight for the 15 foot one for that "roaming round the room" experience so familiar from all those US films and TV shows I watched as a child of the 70's.
Next the daddy, I found on ebay US a 1C2 payphone similar to the one used in the film, from a wholesale buyer who had dozens, waited weeks for delivery but its here, and again the RJ11 as was converted just plugs into a BT convertor.
My bank was less than pleased with the last purchase, you can imagine the postage from the US to UK, then £48 custom duty when I collected it.
I'm working on photoshopping Fight Club "Telnex" dialling instruction cards based on screengrabs from the DVD for this, again I had to ask the folks on Singingwires how to get the plastic fascias off, then I needed to buy a hex set (from US again) to get the nuts loosened.
Lastly, not in the movie, and having become quite enamoured with the Western Electric 500 series I seen a nice red one on ebay US again.
Again cheap to buy and crippling in postage this lovely beast worked fine but the modular case plugs quickly cracked and broke when putting new cables in, so back to the US for replacements, its now the "Presidential hotline" in my room.
The only other money I have expended on them is a set of repro dial lables for the three, I think I've spent enough, would have been cheaper buying them from UK dealers in up and running order, but where's the fun in that eh?
Anyhow now have all my Fight Club vintage phones thanks to a lot of help, research, hours of work and shedloads of money I will never recoup!
To end, I have found the Western Electric machines so easy to restore compared with GPO phones I have still in bits in boxes, really straightforward, just needs a screwdriver and some parts, and an internet connection for help.