"Paul B. Webster VK2BZC" wrote:
>   According to my discussions with the previous poster (I forget
> whether on-list or off now), even acoustic couplers are required to be
> type-approved.

Yes, there are few standards, you can not inject "audio" levels higher
than zero db (or dbm?) at phone lines, according to something I read
many years ago... it could be complete different now... :)