I have been using CompanionLink for a couple of years now with both a blackberry and a Treo. I love it. It works seamlessly in the background and gives you great control over you data. It also allows you to sync Act with Outlook so you can have your data somewhere else. I use the Express version for $49.00 http://www.companionlink.com/products/companionlink.html
Companion Link seems to have a serious flaw. I'm using Act 9 with the Vista operating system. Updates and additions I make on the Blackberry Curve do not properly synch with ACT. The names transfer but the phone numbers do not. In fact, it ERASES the number on the Blackberry, transfers the name only to ACT and the number is lost. This happens EVERY time no matter what settings I attempt to use. Very frustrating.
Mike, the Handheld Contact looks promising, but I couldn't find a price for it. So I downloaded it. Free? Cool. No way. $239 for a year is hardly a solution. It's hard to believe the synch option costs more than the actual program. I'm surprised and continually dismayed that ACT doesn't just provide working conduits for at least the most popular handhelds out there. Give us a REAL solution, please.