It's web-based, so you can view it from any web browser. The free version will let you access it on your Blackberry that way, buti f you'd rather sync directly, the Pro version ($25 a year) has a sync feature specifically for Blackberries.
I've been using RTM for about a year now and it works wonderfully. In addition to the web interface, it has a number of tools to view it from within Gmail, your Mac's Dashboard, and other places.