No. You don't need the 56k modem for a broadband connection.

Yes, previous post is correct. You do not need a 56K modem if you have broadband.  Broadband will connect to the integrated Network port (which the 420 has) from your router or cable modem.  

You don't need one for broadband but very useful to have for using your pc to send fax, as a backup to connect to any ISPs you choose, and for diagnostics. For the few pennies they cost I wouldn't be without one in at least one of my systems.