Attendees try Line Corp.'s new call service displayed on mobile phones at a news conference in Tokyo, Japan.

Japan's most popular messaging app filed for an initial public offering (IPO) in Tokyo, but whether the estimated $10 billion valuation is fair remains in question.

The messaging app, which reported first-quarter sales of 14.6 billion ($143 million), up threefold from a year earlier, earns revenue from advertising, selling stickers and gaming functions, as opposed to other messaging apps that earn revenue from one-off user charges.