You can convert the library to .mobi using calibre. He can read .mobi files using MobiPocket reader, which is a decent reader, and the only blackberry reader I have any experience with.
You can use calibre to transfer the files to his phone's SD card. The software can be configured to convert on transfer, so you don't need to run all of your books through the converter - converting on transfer would naturally make the transfer process last longer.
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