Around 1.7 million phones were sold in September, of which over 600,000, or 37 percent, were feature phones, according to market research institute GfK.

While there have been predictions that feature phones will lose popularity with the advent of cheap smartphones, their sales remain steady at 620,000-700,000 a month, the institute said.

In terms of market share, feature phones even saw a slight increase from 34 percent in July to 36 percent in August.

Nokia remains the leading brand in this segment with a market share of 55-57 percent in recent months, with the Finnish brand accounting for over half of the 20 top selling feature phones in September.

The second most popular feature phone was local brand Masstel with a market share of 14-15 percent. Other brands sold include Itel, Mobell, Fmobile and Coolpad each with a market share of below 10 percent.

Nguyen Duy, an employee at a mobile phone supermarket in Hanoi's Gia Lam District, said: "The main buyers [of feature phones] are usually ordinary workers, students, older people, and businesses buying phones for internal communication needs."

"A significant portion of them are first-time users who want a device that could make and receive phone calls so they could keep in touch, especially one that's easy to use."

Besides, many people buy Nokia's new products such as the 3310, 230 and 105 to use as backup for their smartphones, he said.

Nguyen Tuan Anh, an experienced mobile phone seller, is confident that feature phones would perform well for at least a few more years. 

Since their customers often prioritize low price over brand, phones from China and nameless brands would continue to sell well if they meet buyers' needs, he said.

But revenues from feature phone sales remain low. According to GfK, 70 percent of them cost below VND500,000 ($21.5).

The best-selling device in this segment is the Nokia 105 with a price tag of VND350,000 ($15). Itel, the third largest brand, has products costing below VND200,000 ($8.6) such as Value 100 and IT2161.