Cap, I work for Ma Bell and one of our buildings locally is full of Merlins still in use. These are on an ISDN system--a total nightmare to provision as I can attest to first hand. I'll soon be moving to that building and using a Merlin on a daily basis. At my current desk I've got a Nortel M5316 "EBS" phone and I do like its functionality but again, it's a provisioning nightmare.
On the home front, in my guest room I have an old 202 oval base dated 1931 running through a bell box that I'm thinking is even older as it has wooden terminal blocks. I have a stash of 302's as well, a couple of them with metal cases and brown cloth cords, most of which include the letter "Z" on the dial faceplate, but I have no place to put them. Once I get my home office set up the way I want it, I'll have my early model 500 desk phone from appx 1950 wired up for use there.
These old phones are great, they were never designed to be throw away items like modern phones are. Ma Bell strikes me as the world's original recycler, refurbishing and re-deploying phones for over 80 years before the Bell System break-up changed the way the phone companies did business.