The Bangladesh mobile-phone sector is proving profitable for investors with its quick, high rate of return, according to a study by the National Board of Revenue. The study found the nation's four mobile-phone companies had recorded US$95 million in profit in four years, or about 60 per cent of their investment over the period. Board chairman Khairuzzaman Chowdhury said the companies - GrameenPhone, AKTel, CityCell and Seba - had spent US$150.42 million between 2001 and last year. GrameenPhone, which has a 60 per cent market share, made US$86 million on an investment of US$110.22 million. Two regional giants - Singapore Telecommunications and Orascom Telecom of Egypt - have recently invested about US$318 million in the highly profitable sector. Meanwhile, two much bigger companies - India's largest conglomerate, Reliance Group, and Warid Telecom, a unit of Dhabi Group from the United Arab Emirates - have applied for operating licences.