Check out Mr. Fancy T1 line over here. I remember downloading Slackware floppy images over 28.8 dialup. Talk about pain. I recently stumbled on a dusty box of them whilst cleaning out the attic.
Do you remember the dreaded 'floppy disk is probably unreadable' sound during installation of any software on floppy?
To be fair by the time I 1st used Slackware that 300 baud modem had long been replaced and I at the time I had bonded ISDN channels for 128kbs connection paid for by my employer. Soon replaced by a T1 to my home also paid for by my employer.
Did you employer give you a spec-'d out computer/workstation too? I don't even know how you hook up ISDN equipment, but I know an SGI Indy had it built in.. ~1993.