Chunnu Biswas opened his tiny two-room tin-roofed post office in the morning as usual, but another long day stretched ahead without any letters for him to sort or deliver.

It was the fourth day in a row that the 45-year-old postman in the village of Chowgachi in western Bangladesh did not have any business, and dust lay thick on the large table where he used to process piles of mail.

"Now we are mostly idle," he said. "Villagers come here to chat, not to post letters. Only a few old men write letters these days. Everyone else uses their mobile phones to speak to each other and send texts."

As a government employee, Biswas's job is safe for the moment, but the rapid take-up of mobile phones across Bangladesh has left him and 40,000 other postmen twiddling their thumbs and wondering what the future holds.

Mobasherur Rahman, the director general of Bangladesh Post Office in the capital Dhaka, admits he is worried about how his British colonial-era organisation will survive.

"The Postal Department faces the toughest challenge in its 150-year-old history," he said. "Ten years ago we delivered 240 million letters. It came down to 200 million five years ago, and last year we posted only 150 million."

"Except on rare occasions, Bangladeshi people are forgetting the art of writing letters. Mobile phones are everywhere and very cheap. People just love to call or send text messages."

Bangladesh has some 10,000 post offices spread across the largely rural nation, but Rahman says many of them now get little post for months on end thanks to mobile phones.

The sharp fall in letters has forced the authorities to look for new roles for post offices and the army of posties -- the khaki-wearing men who carry letters to the remotest settlements.

The impoverished country, which has a population of 144 million, had only 1.5 million mobile phones in 2003, but last month had 50 million.

And the number is expected to double by 2015 as the economy continues to benefit from remittances sent home by overseas workers and double-digit growth of merchandise exports.

Also boosting mobile phone use has been the fall in national call costs, from around seven taka (10 cents) a minute in 2003 to just one taka, enabling even poor people to communicate with relatives in other towns or villages.

The impact of emails is another looming threat to the post service, though computers remain rare in both urban and rural areas.

With an annual loss at the Postal Department of 22 million dollars last year, Rahman says the service has to reinvent itself if postmen are to kept busy.

In the past year, his department has signed deals with 16 private banks to carry their remittances to places where the banks do not have branches.

And agreements have also been signed with global money transfer giant Western Union to deliver the US company's money orders through 500 post offices, he said.

"We have also been trying to expand our express mail delivery services to win a slice of the fast-growing official letters and parcels which is currently dominated by private couriers," he said.

Zaid Bakht, economist and research head of Bangladesh Institute of Development Studies, said the post office should make maximum use of its traditional structure.

"There is no other organisation in Bangladesh that has a comprehensive network as the post office. It should utilise its strength," he said.

Rahman has one other plan to keep postmaster Biswas and his colleagues in gainful employment -- a nationwide letter-writing competition.

"We are going to launch competitions titled Writing Letter to Your Friend, A Daughter's Letter to Her Mother or A Son's Letter to His Ailing Father," he said.

"We can't lose this great human habit of writing letters, which I think is one of the most beautiful forms of art."