Ratings agency Moody's has upgraded billionaire businessman Denis O'Brien's Caribbean telecoms firm Digicel.

It now rates Digicel as a B3, rather than a B2, because of Digicel's successful launches and reduced start up expenses in the Haiti and Trinidad & Tobago markets.

Moodys also changed the rating for Digicel's outlook to positive from stable, saying success in Jamaica and its newer markets in Haiti and Trinidad & Tobago, had reduced the company's debt.

Moodys analyst Gerald Granovsky said Digicel is the biggest wireless telecoms firm in the Caribbean and that the company has a successful track record of gaining market share and solid operating results quickly after new markets are launched.