It might be a good idea to try and get your hands on one for a while, to ensure you're comfortable with the PDA as a phone setup. It has it's limitations.
The K-Jam / JasJar and JasJam are all true converged devices, meaning they can perform many functions within one device.
The problem is, as with most converged devices, they're not particularly good at any of them, a decent (but not stellar phone) with decent (but not stellar) PDA capabilities.
The two functions are also in opposition, the better the battery life for the phone, the slower the CPU speed. This is why the K-Jam only runs at 200MHz, to give a decent battery life, but nowhere as good as a standard Nokia.
The JasJar runs at 520MHz, but chows through a battery in a morning if you also use it as a phone, which most people don't. It's main application seems to be a 3G-enabled PDA. Brilliant at this. If I were on the road at the moment, I would've been typing this on my JasJar.
The JasJam seems to sit somewhere in between, a 400MHz cpu with (hopefully) better battery technology and HSDPA.
As a die-hard fan of Nokia phones (and a drawer ful of them), which model do I use for every day use: The K-Jam!
I need the converged PDA capability and it's got one of the best form factors around. I actually type faster on the K-Jam than on the JasJar.
But make no mistake; not a day goes past that I don't feel like throwing the K-Jam against a wall, it's just too slow sometimes....
Can't wait for the JasJam!