I think the SPV M600 is the one without the slidey out keyboard.
If this is the case, then dont get it. The slightly thicker one with the slidey out keyboard is much better for emails and texting.
Not sure what Orange call it, but at O2 it is the XDA MINI S and it looks like this:
The Mini S is pretty cool, with Wifi and Bluetooth. Paired up with a bluetooth GPS, it runs TomTom just fine. Of course, you'd buy TomTom and not download a cracked version from the internet.
Overall, I only use my Mini S occasionally as its a bit bulky. If I'm going on a trip and want it for email, then I'll take it. Otherwise, I'll take a much smaller phone. I'm using one of these at the moment - a Nokia 8800 - very tactile
You'll really like the SonyEricsson K800i when it finally released in the next month or two. 3G with a 3.2megapixel camera. I've been using one for a while now and it is really very cool. Good email client on it as well. Nice and small too.
Andy