The parties are expected to sign an agreement on the joint operation in the country's administrative capital Naypyitaw on Wednesday, according to the sources.
They had initially planned an agreement by May after MPT's decision last year to partner KDDI, a major Japanese mobile phone carrier, but negotiations were extended over budget and human resources issues, the sources said.
The joint initiative would likely involve several billion U.S. dollars in investment, mostly on building and expanding telecom infrastructure in the country where only a fraction of its 60 million people has access to mobile phones.
KDDI would be the first Japanese company to enter Myanmar's telecommunications sector after the Southeast Asian country opened up the market to foreign capital last year.
Norway's Telenor and Qatar's Ooredoo obtained mobile operating licenses after an international bid in June last year. They are planning to start services this fall. KDDI and Sumitomo did not make the cut at that time.
Ooredoo said it plans to invest up to $15 billion in 15 years, while Telenor did not disclose the financial details of its plan but said it aims to cover 60 percent of the population in the first year and 95 percent in the following five years.
Seeing no further room for strong growth in Japan, KDDI and Sumitomo, a trading house, are setting their eye on emerging markets such as Mongolia.