Hmm, Hey guys this is my first post so hey
I have a few thoughts about your 'special idea'. I want to be as constructive as possible so please don't take any of this to hart:
1. Why would new (and old) app developers decide to port the programs they have made to your device? You would have to have something more than a button dedicated to socail features.
2. you would need to make this button easily avalible to the 3rd part programmers by implamenting a special API (which isn't the biggest problem) thus meaning that the developers have to add more code to the program when they could just deploy it to android and IOS with a click of the button with cross-compilers. ;(
3.People seem to like less of buttons. Android has 3 buttons - Iphone has one. if you had 4 where would the 4th button go? 3 buttons at the bottem is perfect - having four would make more issues (Size of device, which order each button gose ect). This dosn't seem like a massive problem, but it is. Acsessability is EVERYTHING when it comes to products, not just OS and mobile devices, so thats one thing to think about.
I have had a little though about this, and here are some little solutions to your idea (Just to get you in the right mood):
1. Use Android OS. You can downlaod it for free, as we all know. It's a little messy to get started with it, but of corse it is possible to make your own Android Device that look compleatly different. All you have to do is strip down the OS to its kernel (Which is linux) and of course the dependecies that will allow for you to run the apk? executables... I think its apk any way (dosn't really matter)
2. You think of a way to get around this. think about it, for 2 secs. You have three buttons and don't want to add another one. You could replace the button sure, but people might get confused... right? Why not add a button to the tool bar??? You prgram the OS to reconise if you are playing a game, waching vids or listening to music. Just bring down the tool bar and you can share the music, game or video by a click of the button. the OS sends a pre-made message to facebook (via API) such as 'Just playing angry-birds' or 'Love 'I got U' listend to it 3 times today ^^' . you catch my drift
This little solution also includes solution to three so
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sorry for bad english and hope I helped