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.