Facebook revealed its smartphone plans Thursday in a development that some industry observers said could shake up how software is presented on handsets. The social networking company and HTC have joined to tweak Android with Facebook's "Home" software, which puts the company's applications front and center on smartphones. Android users will be able to download the software for supported phones starting April 12. "We spend 20% of the time on phones on Facebook," CEO Mark Zuckerberg said. Analysts pondered how many other phone-makers would follow suit, given Facebook's 1 billion global users.