Here's one for the telephone guys

"Hey, you finally figured it out "

Yes, but apparently you haven't. If it doesn;t work at the NTU, it's the phone company's problem. And since you can easily demonstrate the problem to a tech standing there by using a cell phone to call the line, what more do you need?

This isn't addressed to you in particular, Charlie, but IIRC you said you had a NID box, so the last bit may apply. It's general info to others who may have a similar problem.

Another possibility is a DSL filter left over from a previous owner/tenant. When I worked for our telco, I had one call where a filter went short, shutting down phone service. It was installed for a previous tenant's internet.

They get left in place when internet is uninstalled, since they don't interfere with POTS (plain ol' telephone service).

Usually. ;)

Mostly they're mounted near the surge protector, but depending on the phone wiring and/or the internet installer's rush to finish and/or the customer's wishes, they can be stuck in behind a wall plate (phone, not power) somewhere in the house.

If the building has an exterior NID box, it can be located there, too.