Trisha does it for Ajith

Trisha is notoriously famous for her poor Tamil, which has resulted in dubbing artistes being used for all but a couple of her films. However, for Ajith's golden jubilee film, Mankatha, Trisha will dub for herself. Apparently, director Venkat Prabhu and Ajith felt it would be better that way and together they convinced her.

Venkat Prabhu said that Trisha has an important role in the film. He said that the actress shares great chemistry with Ajith and their scenes together in the film are sizzling. Her voice would suit the character perfectly and so he asked her to do the dubbing and Trisha obliged. So audiences can start preparing to hear her particular brand of Tamil mixed with English dialect.

Source: http://www.behindwoods.com/tamil-movie-news-1/aug-11-02/trisha-ajith-09-08-11.html