You can find an explanation for landline in the dictionary as follows:
NOUN:
A communications cable, as one used to transmit telephone or telegraph signals.
Back in the day (as they say) a long time ago..... there was one phone company and they put actual cables, lines, through telephone poles across cities, towns, states, villages, and across countries. These phone lines were the original lines through which people could pick up a phone at one end and talk to someone at the other end.
These cables or lines over time became known as land lines being that (literal translation) they were lines that went over the land. As time has gone by and we have made many transitions and technology has moved in leaps and bounds, landlines have become obsolete. With the advantage of the cell phone and freedom AND free use of VoIP, landlines seem to have started a decline and will someday be a thing of the past.
Not using a landline is also a way of being independent and NOT having to use one of the large companies that are all merging and acquiring each other.
In the beginning there was one company (AT&T) and that company was broken up into six local companies called the "(Baby) Bell companies". The ruling in the mid 1980's by a U.S. court left AT&T with only long distance. But since then, many of the "Baby Bells" have merged together or have merged with other telecom companies. Some have complained that it seems that one day we will be back to one company again. A monopoly. This is a big point that leads many to use VoIP because there are many independent and small companies to choose from keeping the consumer free from having to use a large company with large rates and large bills.
Some complain about the cable companies and how in each state or group of states there is only one cable company to choose from and that they are too big. But some of their packages are too good to ignore. Getting broadband Internet, unlimited phone service, and cable TV for $99 a month is pretty good. The only draw back is that after one year your rates will go up.