Facebook has joined the growing number of companies offering a messaging service for smartphones. The social networking site has announced a new messenger app for Android phones which allows users, including those without a Facebook account, to send and receive messages to and from anyone with a phone number.

Facebook Messenger will allow mobile phone owners with a data connection to communicate without the use of SMS text messaging - which itself celebrated its twentieth anniversary this week. It will also join other platforms such as Apple's iMessage, RIM's BBM, Google's GChat, and WhatsApp, to allow free messaging on smartphones.

The news follows earlier reports that suggested that Facebook was looking to buy WhatsApp - a service which claims over a billion messages sent by its reported 250 million users, every day.

Facebook's app will put it in direct competition with WhatsApp and help the site grow its more than 1 billion active users to the "next billion", a strategy laid out by Facebook chief executive Mark Zuckerberg in an interview with BusinessWeek in October.

"The big thing is obviously going to be mobile," said Zuckerberg. "There are 5 billion people in the world who have phones." 

That mantra has been repeated by Peter Deng, Facebook's director of communications product management.

"We're thinking about mobile first," Deng said at Le Web in Paris this week, as reported by CNET. "It turns our development philosophy on its head."

Facebook Messenger allows users to register and identify themselves using just their phone number, without the need for a Facebook account. Like WhatsApp, the messenger allows users to start group conversations and share photos and is being launched in partnership with mobile phone carriers across the world.

The company said it will begin rolling out the app on devices in Australia, India, Indonesia, South Africa, and Venezuela, with other countries to follow shortly. It will also launch an iOS version for iPhone users soon.

This venture isn't Facebook's first foray into the world of smartphones and apps. In April, the company paid $1 billion for Instagram - an app which allows users to take pictures with their handset, add filters, and instantly share them on social media such as Facebook and Twitter.

The new Facebook Messenger app can be downloaded free from Google Play.