TBH,
I’ve long held that this is the way forward. I’m not really a fan of convergence.
You’ve got a pretty insurmountable problem in that you ideally need a nice big screen for PDA duties but something nice and pocketable to make phone calls on. Until we invent pop-up screens, these are mutually exclusive requirements.
Back in ‘the day’, my Every Day Carry was the smallest phone I could get my hands on (last one I had was a Nokia 6510, the ‘business’ version of the 8310) and a Psion 5.
The Psion 5 was, for its time, a proper workhorse; I could tether it to the phone, albeit slowly, for Internet connectivity, and it ostensibly filled a good chunk of the niche currently occupied by tablets these days. It was small enough to live in a coat pocket, but was big enough (and with a proper keyboard) to do some real work on it. Then when I was going, say, out on the beers or to a gig, I could keep my phone in my jeans pocket and leave my expensive device safe at home.
As a system, for me, it worked really well. Sadly the Psion got long in the tooth and I went through a series of replacement converged devices (O2 Mini-S, TyTN II, couple of early Android handsets) before finding something that came vaguely close to fulfilling promises made for years by manufacturers.
My current phone is a modern miracle, and I’ve waxed lyrical about it before. But I think if someone came out with something like a Nexus 7, the size of a paperback book and in a clamshell design with a keyboard, I reckon I’d ditch it in a heartbeat in favour a Psion form factor PDA and a separate teenyphone.