Its simple and I do it all the time.
Compile your B4a app and test on an Android simulator with similar screen size as your target Blackberry.
Convert the apk to a bar file using one of several tools. Go to
www.crackberry.com for tons of information on converting apk files.
You can now sideload or even submit your app to BlackBerry World app store.
With the next BB OS about to be released this month you can even install apk files directly to the BB phone.
BTW, the Playbook is no different than the phones for installing and any tool for installing on the PB will work on a phone as well.