Thailand's third-largest cellular operator is targeting the service at customers who make limited calls, but they must make a call at least once every 90 days to keep the account valid.

Total Access Communication (DTAC) introduced a similar package last month featuring a one-year validity period.

Like DTAC's promotion, True Move's package charges callers a flat rate of Bt2 per minute.

True Move has 4.9 million subscribers, 4.4 million of who are prepaid users. DTAC has more than 10 million subscribers, most of who are prepaid users.

Usually, prepaid refill cards are valid from a few days to three months, depending on promotions.

Titipong Khiewpaisal, vice president of the largest cellular operator, Advanced Info Service, said the promotions reflected a shift away from the price war that had caused jams in the network connections of all operators.

Some industry observers said that the extension of validity periods is in response to rules expected to be issued by the National Telecommunications Commission (NTC) later this year.

One clause bans operators from setting fixed validity periods for all prepaid services. This is to prevent companies from urging subscribers to quickly use up their minutes before their cards expire.

NTC member Sudharma Yoonaidharma said the trend to extend validity periods would benefit prepaid phone users, who are mostly low-income people.