I read that long article by Sandman, and it makes sense to me. Yes, he's selling hardware to mitigate or solve telco problems, but the advice is still sound. I didn't find any FUD or misleading information there at all.
I don't understand the comments stating it's extremely unlikely that a POTS telco could be at fault. Anything's possible.
The most definitive way to test this is to disconnect your premises (home, office, apartment, whatever) telphone wiring from the telco's service at their demarc box. Assuming that you don't own or have access to a telephone "butt set" or a telephone line 600 Ohm load tester, use an ordinary telephone, preferably an old fashioned "2500" model desk phone, or some other phone that you can remove the case and disconnect the line cord. Put a digital multimeter in series with the telephone line connections (inside the phone, disconnect one of the two wires leading to the modular line cord, then hook up the meter, one probe to the line cord side, and the other to the telephone. Leave the phone off hook. Set the meter to the highest current (amp) range. Plug the phone's modular plug into the modular jack on the telco demarc box. Read the current. It should NEVER be as high as 62mA; that would fry electronics. If it is significantly above 25mA, call the telco and demand that they look into it.
If it is within normal range, then you will need to troubleshoot the OBis. Their built-in voltage and current measurement feature may be bogus or fried on your units, but I have a 110, hardware version 2.8, and it properly reports normal voltage and current on my POTS line.