FWIW, USR Courier modems can be configured for leased-line access - meaning connect the two modems together directly with a phone cord and they'll establish a link. No additional hardware/software required. You can find them pretty cheap on eBay. There are Mac modem cables which have Mini-DIN8 on one end and DB-25 on the other which would be perfect for this.

http://www.usr.com/support/doc-popup-template.asp?url=faqs/analog/leaseline.html&loc=unst