Apple won't market this to the corporate market
If they don't try to get it into the corporate market they'll miss a ton of revenue. Almost everyone I know that has an all-in-one device got it from their employer.
Then it will hardly replace or compete with Blackberry. Nor will it compete with Windows phones for folks who want to display spreadsheets and such.
I personally have trouble imagining the need for this, but I was in a phone store when someone came in to buy a Windows phone. I guess the attraction is that someone else is paying for it.
My personal idea of a phone is something that fits in my shirt pocket and becomes unnoticeable.