A modem is a device that converts the digital information of a computer into analog information for sending over a home phone line.
Most home phones use analog technology.
Also when information comes to your home over this line it must be converted back to digital from analog. Direct access is best because it is fastest and there whenever you want to use it. Cable TV companies are starting to over this service. The most common type of access is difficult to gauge. Business and schools almost always have direct access, most home users almost always use modems.