B&N Reader apps currently only read eReader ebooks. The Nook is their first device to support ePub as well.
Shortcovers has its own BlackBerry reading app, which should be able to download and read your titles from them.
Calibre can convert DRM-free ePub to eReader. If your ebooks have DRM (encryption), see Adobe ADEPT DRM for EPUB circumvented
. Note that stripping DRM from ebooks you bought for personal use is probably legal in the US (for example).