Is there an adapter to connect a iPhone to a phone jack?

Basically can you hook up a aux cable to a corded landline telephone?

There's, but probably not in the way you think. Http://mashable.com/2012/09/02/iphone-docks-desk-phone/#

Anything is possible with Bluetooth, so I would guess you can keep looking for a bluetooth to analog adapter to physically use a whole corded phone with an iPhone.

I would have said, "No Way!" But our friend Carl N has found something that really answers the call!