If this an app hosted in a browser, Blackberry respects WAP conventions for encoding a phone number.
Here's an example snipppit for displaying a number that is callable via a Blackberry device:
<a href='wtai://wp/mc;5551231367' title='Call'>555.123.1367</a>
I've been using this approch for some time now and it works for me. When the user clicks the link, a dialog from the OS pops up and asks if you would like to call this number.
Additional Information
I also recommend checking out Blackberry's additional resources on development. Since the current browser is still in the stone age compared to iPhone/Android it's worth seeing what's possible.
http://na.blackberry.com/eng/support/docs/subcategories/?userType=21&category=BlackBerry+Browser