I worked for RIM for 2 years on an internship. The BlackBerry has come a long way in the last few years. Have you tried developing for your Pearl yet?
What sort of data plan do you have?
So to answer-- I've had the 7200, pearl and 8700 as my primary work device. I still used my Windows mobile phone most of the time though (off of work), as it was nice not to be attending to work email all the time.