I manufacture an automatic phone line switch. Recently an enterprising young man discovered an application where he brings line 1 and line 2 to the Combine-a-line switch
and then to his dsl modem. Another port enables connection of any SINGLE line phone appliance (telephone, fax, computer modem ,etc) and that single line device will automatically work and give access to both phone lines!
I have several on Ebay and thanks for looking