New Delhi, Nov. 7 -- Tata Sons Ltd has ploughed over a billion dollars into its iPhone assembly business since inception, helping it cross watch-and-jewellery brand Titan Ltd in revenue in just four years.

The Tata Group holding company last month invested Rs.1,499 crore in Tata Electronics Ltd, its phone assembly and semiconductor venture, bringing its total investment in the business to $1.3 billion. This also makes Tata Electronics the third Tata Sons subsidiary-the others are Air India Ltd and Tata Digital-to receive over $1 billion from its parent in the last four years. Tata Sons' investments in the three businesses now total $11.1 billion, a Mint review of the filings of the three subsidiaries showed.

Tata Sons' latest annual rep...