It's a pain to connect a blackberry with a Mac. My suggestion is to use Google Sync in conjonction with gmail. That way you never lose contacts no matter which OS you are running.
It's really easy if you're willing to spend a few dollars on markspace's missing sync application. I used it with my old palm treo, my old blackberry curve, and now my blackberry storm. It's worth the money, but you'll still need a PC if you're planning on upgrading your blackberry software or installing new apps.