Mobile messaging service WhatsApp hopes to introduce paid subscriptions for iPhone users this year.

Jan Koum, WhatsApp’s chief executive, revealed his iOS intentions to Dutch journalist Alexander Klopping. The new subscription model, which applies to new users only, will most likely be free for the first year and then cost an annual $1. At the moment, iPhone users are charged a one-off $0.99 for life-time use.

An iOS subscription model would bring WhatsApp charges in line with other mobile OS platforms.

Techcrunch, which obtained an English version of Klopping’s interview, reveals Koum as having no fixed dates for introducing the new iOS charges. “We’re relaxed on dates, but definitely this year,” he said. “It’s on the roadmap.”

WhatsApp is coy about giving a breakdown of app downloads by mobile OS platform but, as reported by Gigaom, WhatsApp passed 100 million downloads on Google Play last November. According to analytics firm App Annie, cited by Gigaom at the time, WhatsApp was the top overall paid app in the Apple App Store in 119 countries, as well as the top paid social networking app in the US.

WhatsApp announced last August that it hit a new daily record of 10 billion messages sent and received in a day. That’s up from 1 billion messages a day a year ago.

The rise of online social messaging services on smartphones has proven a drain on operator turnover. A report last year from market-research firm Ovum estimated that operators, by 2016, will have lost $54 billion in SMS revenues due to the growing popularity of online messaging.