Your squeal will only go to the first exchange on the way, where it WILL be digitized and sofware-limited, or even hard clipped right on the analog line if necessary, and then sent through to the other exchange, where it will be amplified by an amp again with limited output levels.
there is no way your high level squeak will get to the other side with the intensity you expect. It may be fairly loud and annoying, but I doubt it would be ear piercing or anything like that.
Isee your point . I don't expect anything I am looking to get the loudest effect I can at the other end . Some people know what they are talking about and some don't
But if you are so desperate to try it, connect some audio amplifier to the line through a capacitor (non-polarized, large value) and see what you can get. Disclaimer: the reponsibility for burned amps, houses, etc. is only yours
This is what I will do but I seek knowledge or experience of what circuit might be tuneable to give this effect