networking – How can I get a 56k modem as a server using DSL?

I want to run an old school BBS system using a modem, and accessible to 33.6 and 56k users

I know there are technical differences with modems that go over POTS PSTN networks and that regular modems work up to 33.6 k and a DSL or fractional T1 is needed for 56k downloads over analog modems.

Can anyone educate me how to upgrade a 33.6 modem into one that supports 56k line?