(Also see this FAQ for other options and configurations: /faq/10443)
•Obtain a splitter - You can purchase a splitter from Wilcom (1-800-222-1898) for about $35. An information sheet can be found here. Any splitter must have a 4000hz cutoff to be compatible with Ameritech's (ASI) network.
•Run a wire from the Network Interface Device (NID) to the splitter - Use the best grade of cable you can obtain -- best if it is Category 5 or better. Also, keep this run as short as possible, for this is the one that carries both the DSL signal and the POTS signal.
•Plug the DSL Modem into the splitter - Plug the DSL modem directly into the splitter, or run additional wire close to the DSL modem. Again, this wire should be of the highest quality (Category 5 or better), since any interference here directly affects your DSL quality.
•Wire from the splitter to the phones - Plug the phones directly into the splitter, or run a cable from the splitter to the phones.
•Remove any installed microfilters - If you have installed any microfilters to support your previous installation, remove them -- they are no longer necessary.
Below is my current installation, for a visual reference: