Is anyone aware of a device that will convert a US POTS phone line to "standard" audio inputs and outputs?

I'm trying to connect a video conferencing system to our phone system so that people who are remote can dial into a phone number and listen and speak with the other conference attendees. The video conferencing system has a 1/8" phono (TRS) jack audio input and RCA audio outputs. But any device that gets a phone line converted to any standard audio format would work.

The device would have to have some smarts, most likely, so that it would only pick up the line when someone else has first, or activated with a switch, or something. I suppose I might actually be able to do this with a computer with a voice-enabled modem. But a standalone device would be cool.