What I learned is that blackberries render differently based on the type of blackberry, os version, screensize and settings like email set to text or html, etc. The most success I had was to keep the report page size as 8.5 by 11 and send the report as a PDF attachment. PDF's seemed to render consistently on all the blackberries were are using.
Also, want to try to limit the number of columns in your report if you can. If you can limit the report to 6 columns or less that would be ideal. You may need to use a fairly large font size as to fill out the blackberry screen better like perhaps an 18 or 20 pitch font. Otherwise, the blackberry user will need to zoom and scroll to read the information. You may need to do some trial and error testing on mulitple blackberries to achieve the look and layout you desire.
While it is possible to get a report send in mhtml format to render well on a blackberry, I found the report will render completely different on other types of blackberries.
Good luck!