Re: Why do land line telephones have alphabets on the number keys?

Philipp Reis invented the first functioning telephone ("telephon") in 1863 ( http://german.about.com/library/blerf_reis.htm)

Alexander Graham Bell eventually commercialized, in 1876, an apparatus better able to transmit human speech, but that derived from the work by Reis and Elisha Gray. It was soon used as a subscription service with the invention of the telephone switch or central office. Such an office was manned by an operator that connected the calls by personal names.

The latter part of 1879 and the early part of 1880 saw the first use of telephone numbers at Lowell, Massachusetts. During an epidemic of measles, Dr. Moses Greeley Parker feared that Lowell's four telephone operators might become ill, leading to a loss of telephone service. He recommended the use of numbers for calling Lowell's more than 200 subscribers so that substitute operators could me more easily and rapidly trained in the event of such an emergency. Parker was convinced of the telephone's potential, began buying stock, and by 1883 he was one of the largest individual stockholders in both the American Telephone Company and the New England Telephone and Telegraph Company.

Even after the assignment of numbers, operators still connected most calls into the early 20th century; "Hello, central, get me Underwood-342"

Connecting through operators or "central" was usual until mechanical dialing of numbers became more common in the 1920s.

In North America, the digits 2-9 of phone numbers were alloted 3 letters of the alphabet apiece.

Phone numbers were not usually strictly numeric until the 1950s. From the 1920s until then, most urban areas had "exchanges" of two letters, followed by numbers. This was considered easier to remember, although in the later part of this period it required the memorization of 7 characters (the same number of characters as is usual for local calling in 2003). A word would represent the first two digits to be dialed, for example "TWinbrook" for "89" ; "BYwater" for "29"; 736-5000 was "PEnnsylvania - 6- 5 thousand".

(Courtesy: http://psychcentral.com/psypsych/Telephone_number.)

Also, you can Google for history of telephone alphabets and numbering for further insight.

I hope it helps.