iphone slider keyboard

Business blackberry user is due a phone change and is fed up with their crap web navigation but really needs a good keyboard for business emails and efficient texting.

User wants iphone or similar smartphone for web usability (and fun) but knows it will be hopeless for typing business emails.

I've just spotted bluetooth keyboard cases for iphone4 and wonder if any have tried them and are they any good?

eg (a slider case):


or http://preview.tinyurl.com/6ogvrr3

We're not too impressed with the current offerings of physical qwerty keyboard phones.
it's a ba-na-na . . . .