Why were the Q qnd Z the two letters missing from the old telephones?

Answer 1

Telephone numbers were once assigned letters to make them easier to remember. The letters represented the area the number was assigned to. For example SYcamore 4 or Pennsylvania 6. The letters Q and Z were not included because they were the least common letters to be used.

Answer 2

Phones from as early as the 1930s do have all of the letters: Q was on the 7 with PRS and Z was on the 9 with WXY. These letters were used in some of the trunk prefixes in the US that were abbreviated as two letters in front of the line number (e.g. Quincy: QU-3456, Beachwood4: BE4-5789).

On some, there was no room for them on the dial pad and they are the two least used letters of the alphabet. And there was no texting with old phones.