I don't know, definitely too big for me to use one-handed but I've got a mate with a Dell Streak and he can use it one-handed comfortably!
He still doesn't though, he just uses it 2-handed all the time. In fact you know what folks, I'm not even sure people care about one-handed operation, or that it's even possible with touchscreen phones. In my experience, I only ever need to use it one-handed if I'm walking down the street and carrying things, and trying to type on a touchscreen with one hand is just too difficult without any tactile feedback on key presses, without being able to rest your thumb on the phone even lightly cause you'll trigger the touchscreen, without a raised surface of keys to slide your finger over so you can find the key you want to press by touch rather than having to look (crucial when walking in the street unless you want to get run over, and that's the only time you'll use a phone one-handed really). So even though my Desire Z fits comfortably in my hand, if I have to use it while walking I'm actually better off sliding out the physical keyboard and using it 2-handed - at least the feel of the keys means I don't have to be looking down at it all the time. If I HAVE to use it 1-handed (say if I'm carrying stuff) Gesture Search does a decent job if I'm looking for a contact to call, but for typing messages and things voice recognition will just need to get A LOT better than it is now, as I'm not convinced that 1-handed touchscreen typing will EVER be comfortable!
So, having established that people can't use even normal phone-sized touchscreen devices one-handed, why not go bigger? What've you got to lose? In fact stylus input might make 2 handed operation easier than that awkward thumb-typing! Not saying I'd get one, but if your pockets are big enough or you carry a briefcase or a European-style manbag you can put it in size won't be a deterrent.
I honestly am not sure what you're comparing it to when you say "communicator style" phones because they haven't really been sold for a few years in the EU and the only one to generate even more than a blip was the DesireZ in terms of communicator formfactor. If you mean smartphones as a whole then the only one that has been this large so far was the dell streak and it didn't exactly set the world alight.
Well you gotta admit though, they receive very little marketing and almost nobody carries them. In this country it was only sold either SIM-free or from CPW and its subsidiaries as far as I know (online at least - never actually saw one in their shops!). They hardly bother to market them at all as they figure they'll get a few guaranteed sales from diehard keyboard fanatics who are desperate enough for one to look for them. The only hardware keyboard phones (apart from Blackberries) who received any significant exposure were the Milestone/Droid (and that too not so much over here as in the States) and that recent Nokia one (the one that looks like the N8 but with a keyboard). VERY few ads for the Desire Z about. I'm pretty sure more would get sold if people were aware of them or you could actually find them in the shops!
I miss my old Universal though, now THAT had a keyboard! People actually stopped me in the street to comment on it, used to try to fool strangers into thinking it was a laptop. I'd restart it so they could see the Windows logo, and I'd tell them the SD card slot was a "micro-DVD player"!
And no, there was no chance I could use it one-handed!