Use your favourite method to download the com.bbm.apk file from Google Play and transfer it over to your device, for example trough the browser or e-mail it to yourself. It should install and run just as you would expect on any android device.
I've just done some quick testing, but a couple of minor issues came up:
- Needs to be running, background service does not seem to work. I don't know if this is a limit of the runtime on the Jolla or something else.
- Reading of shared QRCode PINs using camera fails.
Need more proof ? Checkout this short video demonstraing chatting with a Jolla and a BlackBerry Z10.