Palm Treo > BlackBerry. My first BlackBerry was the 7230, and then the 7730 and the 7105t. Then the multimedia bug hit me.
BlackBerry > Nokia N95. But it turns out I didn't use the multimedia stuff and was spending all my time trying to make the Nokia better at messaging and PIM. I tried the E71 and E90 from Nokia as well. Better, but not BlackBerry caliber. And that E90 was a freakin' brick!
Nokia > BlackBerry. A homecoming of sorts. I jumped on the 8100, moved to full QWERTY with an 8300 and finally the 9000. But my curiosity got the better of me and I made another switch.
BlackBerry to Palm Pre. That lasted just long enough for me to get the factory rebate on the Pre, which I wanted to keep as a backup and to watch the development of WebOS, but the Pre felt like a beta release at best. None of the promised apps available, no customization options for email alerts, and no unified inbox for multiple accounts. Again I found myself trying to turn the Palm Pre into a BlackBerry which was both futile and stupid. So, back to RIM.
Palm Pre > BlackBerry. I even ported from AT&T to Sprint for that Palm Pre, but after going back to BlackBerry I stayed with Sprint. 8330, 9630, 9650. Once again, the lure of something new and different has me experimenting. This time it's Android.
BlackBerry > Samsung Epic 4G. 4" Super AMOLED screen. 'Nuf said. I've got to try it. A couple of co-workers have Moto Droids and rave about them. I was all set to grab an EVO when the Epic 4G came out. After checking them out side by side it was close, but the need for a physical keyboard was the tipping point. My BlackBerry is never far away though. In fact, it's in a charging cradle on my shelf, poised to come back into service.