This thing is easily unlocked, so you can put any SIM into it.
The SF is causing quite a stir at the moment. Right now it's sold exclusively by Orange and there is a healthy ebay buzz going on, with that thing being bought like mad from all over Europe. I've heard from people flying to London from Germany to buy one, this still being cheaper than buying some overpriced HTC phone around the corner...
It's really cheap as chips and quite good for that. 512MB of RAM, a 800x480 OLED capacitive touch screen, GPS, 3G, WiFi, FM-radio and all of this in a nice thin package. The battery is a bit on the weak side, though. And the camera the usual crap. Still, you can't get a better budget smartphone right now.