It's been the talk of the mobile world for months, but only now do we know what Facebook Home offers.It's the Facebook Phone, but on various existing Android phones, as well as a new one. But strictly Android. Facebook Home is not going to happen on iOS, specifically because the software, given the chance, takes over the homescreen of your smartphone. Something Apple is unlikely to be comfortable with.But Google is good with it, if that's what you want. Facebook Home will be available on the newly-launched HTC First (more on that later), as well as the Galaxy S III, Galaxy S 4, Galaxy Note II, HTC One and HTC One X+. Other models should follow, as well as tablets, according to Facebook. As for a launch in the UK, it should be offered via Google Play for those phones in a matter of days.All well and good, but just what is it? Well, Facebook Home is the next generation of Facebook on the go. Load the full version and you'll experience updates and information from your news feeds on the lock screen of your phone, automatically scrolling through updates, with an option to skip through faster if you wish.You can also interact with those updates ('like' for example, as well as the ability to comment), with notifications popping up on top of that Cover Feed, which gives access to relevant Facebook apps to reply.If someone sends you a message, these pop up within a circular profile icon, showing part of the message. If you tap 'Chat Head', you can talk to a contact too, without leaving the app you are using. Talking of apps, you can still easily access all your apps, as well as a a selection of Facebook-related apps, should you want to stick with that network.It really does turn your phone into a Facebook phone if that's what you want, although you can limit its role, if that sounds a bit 'much' (or not install it at all, if you don't think much of Facebook). Manufacturers seem comfortable with the concept so far, but other app makers might be less convinced. After all, Facebook Home offers a separate eco-system for fans of the network, one they might not leave too often once installed.