TTK first
trademarked the name Sony (for a
transistor radio) in 1955 and made the official corporation-wide
switch to
Sony Corporation in 1958. The name comes from
Soni-tape, a product the electronics company had been making since 1950.
Akio Morita switched the last letter to 'y' for the company name because he felt that the English phrase '
sonny boy' conveyed a "youthful energy and
irreverence he wanted at the heart of the company."
1 The connection is more obvious when the phrase is spoken by
Japanese tongues, as the "o" is spoken as a
short vowel in
Japan.
I doubt the company would have been near as internationally successful with the name Tokyo Tsushin Kogyo.
1. Nathan, John. Sony: The Private Life.