The whole idea of onscreen keyboards is flawed. Due to being onscreen.
They take up half the space. And you're never sure which keyboard layout you're gonna get. Or what the Enter button will do (will it take me to next field? Backwards? An OK button?). They also usually pop up and hide whatever action buttons are available on the page/app. And no touch feedback (not talking about haptic, I mean actual fingers-across-keys touch). Give me the keyboard from a Wizard or TyTN II over even the best swypey onscreen nonsense anyday.
This is SO true. Every word of it.
I've actually still got my Wizard, and my wife and I both still use it, just not for a phone. We use it for Grocery shopping using the Handy Shopper app. Still nothing as good as the old Handy Shopper on iOS, Android, or WP. For that, I have to keep my old Windows Mobile 5 phone. Plus, the keyboard is backlit. Must have for physical keyboard on a phone.
They must implement the new way, Surface style, like phone cover and keyboard.
Not for me, thanks. It would be a constant battle flipping it out of the way to answer the phone. For a tablet, it's the best possible solution. For a phone, not so much. I want a slider that stays out of the way until I need it. Don't want keys across the bottom, that also takes up screen area.
The arrow keys/D-pad were also very useful, along with the call/end keys. It is really a shame that absolutely everyone followed Apple and there are almost no physical button devices today.
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Working with Outlook and MS Office was also easier: I had the entire screen to see, with keyboard for typing, and stylus for precise selection of word/paragraph/cell.(That is aside from the fact that Windows Mobile was way ahead of its time, and even today is in some ways ahead of WinPhone 8 for productivity)
^^THIS! I'd still use the wordflow keyboard for a quick text, or the speech recognition, but for working in Excel/Word/Powerpoint/Outlook, I need a physical keyboard.
Please enough with the "slimmer" already.

Thick. Fill it with battery. Review, make thicker, add more battery. Sell smartphone with real-word full day battery life. Take all the money.
I actually liked the design that Microsoft abandoned where it had the slide-out keyboard with interchangeable parts. It could have the keyboard, or swap that out for a game controller with D-Pad and buttons, or swap that out for spare battery power for extra juice on the go. I would SO buy that with a 6" screen and USB-OTG.
Actual keys. Not Touch Cover ones. And remember the little dots or ridges on a couple of the keys that allow you to truly touch type. But illuminated is good too.
Illuminated isn't just good, it's a must have. So are the bumps. Can't touch type without bumps or ridges.
So I am going to chime in here with a contrarian view. Having got the hang of Word Flow (on my WP devices) or Swype (on my Nexus 7) I for one do not wish or long for a physical keyboard. Also I use the talk to type feature on WP and Android quite a bit as well so for me a physical keyboard is not something that I pine for.
This is coming from someone who used a HTC TyTn II for 40 months straight, the longest streak for any smartphone in my stable. The second longest streak is a Lumia 810.
This comes from people who don't do touch typing. For people who want to do actual office work on their phone (corporate types, I suppose, or me) and who are also adequate typists, no touch flow keyboard on screen can keep up with actual typing. I can type 50+ words per minute on my old HTC 8125 Wizard, and that is a REALLY small keyboard.
I can get messages done a lot faster than speech recognition, because I don't have to go in and correct errors and insert correct punctuation, etc. Yeah, I make sure texts are "mostly" grammatically correct and spelled correctly. It's called "Grammar OCD" and I'm proud of it.