Unfortunately Blackberry doesn't support calendar subscriptions the way most other phones do. A couple work-arounds you might try:
• The mobile version of Full Slate should work on any phone running Webkit, which is included in Blackberry 6. To try it out, just go to m.fullslate.com on your phone and log in using the same password you set on the web.
• Full Slate offers real-time, 2-way sync with Google Calendar. You could use Google Calendar as an intermediary between your Blackberry and Full Slate. This article explains how to sync Google Calendar with Blackberry: http://support.google.com/mobile/bin/answer.py?hl=en&answer=82619 and you'll find instructions for setting up a Google Calendar sync in here in the Help Center.
Please be aware that anytime two disparate programs are connected, it's not possible to guarantee 100% accuracy. As a result, we recommend not fully relying on a sync or subscription to operate your business. The safest approach is to check your schedule directly on Full Slate, whether on the web or mobile.