While all three will remain stand-alone apps, at a much deeper level they will be linked so messages can travel between the different services.
Facebook told the BBC it was at the start of a "long process".
The plan was first reported in the New York Times and is believed to be a personal project of Facebook founder Mark Zuckerberg.
Once complete, the merger would mean that a Facebook user could communicate directly with someone who only has a WhatsApp account. This is currently impossible as the applications have no common core.