Gil,

You have just described a SLIC!

OK, not a full-feature, all-singing, all-dancing, bells-&-whistles SLIC, but it is still a "SLIC" - Subscriber Line Interface Circuit!

BTW: in some territories, connecting unapproved (including homebrew) equipment to the Public telephone system is ILLEGAL.
And with 70VAC, it's not to be taken lightly anyway!