For WhatsApp, Android is king. About 73 percent of WhatsApp users are running the Facebook-owned communications app on Android devices.

The breakdown of WhatsApp users across devices comes from new research by the GlobalWebIndex, a market research firm on the digital consumer. While iPhone remains the popular go-to first step for app developers, Apple devices only make up 22 percent of WhatsApp product users.

Windows Phone also capture a significant percentage of WhatsApp users. Only 3 percent of phones worldwide are on Microsoft's system, according to the International Data Corporation, yet 10 percent of WhatsApp users run Windows. The remaining significantly percentages fall to Blackberry at 4 percent and Symbian at 3 percent.

But the user base, especially for iPhone users, could significantly grow over the coming months. On August 19, WhatsApp opened their web service -- WhatsApp Web -- to iOS clients. That means people using iPhone and Mac devices can access WhatsApp messages on desktop and iPad via a web browser. With that update, Apple users can more easily sync messages across systems.

WhatsApp has also worked to innovate its current Android product. Earlier this month, WhatsApp for Android added mark as unread, custom notifications, muting chats and emoji skin-color variations, The Next Web reports. The messaging service continues to compete for market share with Facebook's own Messenger, texting native to phones, WeChat, Kik and other messaging apps. 

Facebook has 1.49 billion monthly active users as of June 2015. In its second-quarter report for 2015, Facebook also announced user numbers for WhatsApp, Messenger and Instagram.

Launched in 2009, WhatsApp allows smartphone users to text, call, video and send audio messages over the mobile app. Facebook purchased the company for $19 billion in February 2014. At the time of Facebook's acquisition, WhatsApp boasted 450 million monthly active users. That number jumped to 700 million in January 2015. Facebook CEO Mark Zuckerberg reported his company’s second-quarter earnings in July that WhatsApp now has 800 million monthly active users -- approaching the 1 billion milestone.

The GlobalWebIndex study polled 12,606 WhatsApp users, aged 16 to 64 years old. Respondents were able to choose more than one device option if they owned multiple phones.