Ok, so Android is open-source as mentioned already by other comments.<p>Now the thing with Android is that, it is just a framework, so saying Android is Open Source is missing big points
There are two major limits:
1. What about apps?
2. What about drivers?<p>Today, if you get an Android phone with Google Apps, especially Google Play Store, you have access to many tools that can be considered useful for everyday use, which you won't have with FOSS Android. Here are some examples:<p>With Play Store, you can have (mostly?) any IM, as long as you install the app going with it. The only possibility I know to do that with FOSS Android, is to use matrix or IRC, and have server-side libpuprle connectors.<p>With FOSS Android You don't have factorized push socket: Most apps pushing notifications on Android require GCM. But even if it doesn't require GCM, there is nothing fully open-source an app developer can use. All they can do, is open a socket to their own server, and deal with it, which is a huge battery-killer.<p>Many people are mentioning f-droid as an alternative to Play Store. I'm sorry, but I consider this a joke. I highly respect the work done on f-droid, but this is not a usable alternative.
For instance, you want to save your SMS. We call that backup, but not every knows that.
Well you search for "save sms" on f-droid. No result.
You search for "save sms" on Google Play Store, the second result is SMS Backup+ which is open-source! You search for SMS, the result is on the first page.
Same thing happen if you just search for "sms", QKSMS (an opensource SMS application) is much easier to find with Google Play Store than f-droid.
Even to look for open-source apps, you're better off with Google Play Store!
Again, I totally respect F-Droid devs, this is this way because of their choice of not tracking or saving any user information at all, which is legit.
But then, some people might want something intermediary. Just counting the number of installations of an app can be really useful to better sort apps (SMS Backup+ and QKSMS really deserve to be among the top in the results for SMS).<p>Now, about the drivers. Yes Android is open-source, but good luck running a phone with a FOSS Android!
At the moment, you have the choice with either replicant, which is old and missing gpu acceleration, or running a mainline Linux kernel with Mesa & stuff, but then you have no radio.<p>Though I have to mention that on the drivers side, Sailfish OS and Ubuntu phone have also those problems.