I would like to change my DSL provider from my local ISP, who actually buys the DSL service from BellSouth (BS), directly to BS. I want to minimize any down-time without DSL, so I was thinking that I would order DSL FastAccess from BS and then when the modem from BS arrives I would swap it out with my ISP modem and configure it and get it working. Then I could cancel my ISP DSL service. Prior to canceling my ISP DSL I would therefore effectively have two DSL services over the same line: with the service being determined by which modem is connected. Of course, only one modem would be connected at any given time.
Would that procedure work or do I have to cancel (shut down) my ISP DSL service first?