I will start by saying this is mostly a question of curiosity. That being said, maybe I'll learn something I didn't know. I have a pile of line cards, better than 50 I would guess. Some are ITT 400E cards, some are specialty cards like tie lines and manual icom cards, but the majority are 400D of various issues. What I'm curious about is; Does anybody know what changes were made to each issue? Was/is there some document that spelled out all the changes over the years? I know issue 15 allowed for bridged ringing, where all issues prior were grounded ringing. This mattered to me because I have a bunch of VoIP lines, and we all know how that goes. However, on my copper POTS line right from Fairpoint, all the other issue cards work just fine. They ring up, hold, release, and do what line cards do with equal aplomb, at least as far as I can tell. I haven't left them in for extended periods to see if they have issues with phantom ringing or some other wonky trait. I do know that the issue 14 card I have in there now works splendidly considering there is a rotary set on the line before the KSU. The pulse dialing doesn't make it falsely ring up or anything. It seems to just plain work. I guess that was the point, but obviously they had to be changing something to come out with 15+ versions of the 400D card. I'm guessing 15 was the last, since I've never seen a 16. Seems like the stuff Western Electric came out with after the D series just sucked. I refuse to use the G and H cards I have.
