I decided to get the Dell Streak instead of a HTC Desire, and to use it as my main phone.
It's a dell and less likely to break, on here the battery life looked (and has since proven to be) longer than most of the new phones out there, and there's more breathing room for apps on the NICE display.
I knew before I got this tablet that it would be a lot bigger than a standard mobile, but the Streak actually surprised me by being reasonably light and slim. It's about the same size as a gamegear for those that remember the 90's, and fits into my suit pocket!
The best thing about Streak is you can view whole websites on the display - trust me it's a lot easier to browse on than a standard smartphone screen (I've had enough of squinting at my old one over the past couple years)
Then there's the Android Market. I got Streak knowing that it was yet to get the 2.1 update, but even though I'm looking forward to using the new Android features I actually have no problems with 1.6, so far anyway. All of the apps I've wanted to download have been compatible - I'm using Spotify Premium for music, Beeb player for TV shows (by the way, Streak is REALLY fast over Wi-Fi) and Last.fm for getting through the office slog!
You probably just want to know about how the phone calls thing works - that was my main stipulation before buying. I use a bluetooth headset with my Streak - it's comfortable to wear and no one even notices I'm using it. You can hold streak up to your ear, but I tend to leave my headset in.
So, after two weeks of using my Dell Streak I'm definately impressed - the battery lasts me all day, (I see my mate recharge his fancy smartphone at lunch and think haha!) and I've really enjoyed the web browsing experience. Two thumbs up - for me this is the perfect balance between an unweildy ipad and a too-small phone.