Investment in Bangladesh's fast-growing mobile phone market is set to jump 21.43 percent and top $3.4 billion in the year to June 2008, the Asian Development Bank said on Sunday.

Bangladesh's six mobile phone operators added 1.41 million new subscribers in April, lifting the user base to 40.34 million, according to the latest data from the telecoms regulator.

"Increased demand for mobile phones, aided by affordable service from multiple operators, is the key driver of the growth in the industry," the ABD said.

Although nearly half of its people still live on less than a dollar a day, Bangladesh has been one of the world's fastest growing cellular markets, with a mobile penetration rate of more than 26 percent.

It said the significant fall in handset prices and lower duties and connection fees in the last few years have enabled low-income groups to buy.

Bangladesh has the lowest average monthly cost for mobile telephone use at all levels of use -- low, medium, and high -- for prepaid and postpaid tariff plans, the ADB said, referring to a recent report called 'Mobile Benchmark Studies in South Asia and Latin America'.

Bangladesh's cellphone carriers are GrameenPhone, majority owned by Norway's Telenor; Egyptian Orascom Telecom's ORTE.CA Banglalink; AKTEL, majority owned by Telekom Malaysia International; CityCell, a joint venture between Pacific Bangladesh Telecom Limited and Singapore's SingTel; Warid Telecom of the United Arab Emirates and state-run Teletalk.

Grameenphone leads the market with nearly 18 million subscribers followed by Banglalink with more than 8.5 million.

Several market surveys have forecast the number of mobile phone users will be around 70 million by the end of 2011.

Mobile phone services are an important contributor to the cash-strapped nation's economy.

The sector directly employs more than 15,000 and indirectly creates jobs for 650,000, the ADB said.