AT&T lets you change your home screen with any non-Apple phone. I don't know of any restriction from Verizon (I run SPB Mobile Shell on my Verizon phone), T-Mobile, or Sprint.
The restriction on the home screen is purely from Apple, the carrier isn't involved at all.
My point is that even though the core of Android is open source, the users DO NOT get the open source experience.
Rooting is always possible, allowing you to get the experience you want. And you can always download new apps to change the experience, and developers can create those new experiences.
Except on the iPhone. Apple's restrictions on even what kind of app you can develop inherently limits the experiences available for the iPhone users.
Between proprietary closed-source apps making up much of the standard delivered OS experience
Which you can override with other apps...
proprietary user interfaces (both of which have resulted in legal threats against Android developers)
Which you can replace (and I would love to know about those legal threats against developers of alternative UIs - I've not seen it)...
and hardware locks
Which have already been bypassed, because the OS is open source so the developers can see how to get around it with new versions...
you aren't that far away from the iPhone.
Simple question: can I create a new home screen on an Android phone?
As an Android developer, there is ZERO requirement to get Google's blessing when doing an app. That's a HUGE difference.
You can root an iPhone and do it too. If I install Ubuntu, I know I have full open source. I can do anything. Not so with an Android from your carrier.
Which you can replace (and I would love to know about those legal threats against developers of alternative UIs - I've not seen it)...
Which have already been bypassed, because the OS is open source so the developers can see how to get around it with new versions...
The same gets done with the iPhone, thus my point: You have to root/jailbreak either to get your freedom.