It's not quite that bad. The thing you need on one end is a digital modem. You can buy a card containing a bank of these for the Cisco ISR G2 platform. The ebay cost is about $60. Then in the same router, you can put a T1 card, which the digital modems will use to accept calls (costs about $15). Finally you can buy an analog modem card (costs about $20) to accept calls from another modem. All of this would be contained in 1 or 2 rack units.

There are other methods but that's the one I would use. To see one of the other methods, try here: https://www.youtube.com/watch?v=yQ_hWS6ked8