Landline can include cable, DSN/DSL, and fiber. I much prefer any of these to WiFi or cellular ... the landline is faster/wider bandwidth, not powered by a dinky battery, isn't subject to radio interference (or radio eavesdropping, if you're one of those paranoid guys), and doesn't apply extra charges (per minute, per minute over the cap, per cubic lightyear if you're roaming/longdistance, per MB transferred up or down, per MB above the cap, per webpage, per ringtone, per spam message, etc etc). Yes, there's some landline ISPs who'll try to rape you with extra charges; they can blow because there's plenty of alternatives.
56K is for losers. Unless you're on the space shuttle, where 56K is cutting edge and really cool. Or you live in some place faraway from civilization that the landline providers still quarantine as a medieval wildlife preserve.
Tethering is good for mobility. Tethering is slow, inefficient, and expensive when mobility is not required and landline options are available. Plus if somebody leeches your bandwidth you can just pick up a baseball bat and follow the wire straight to their computer room.