I had the original jolla phone. Fun device and great for starting out developing simple apps.

Back then they had a 3rd party whatsapp client called mittäkuuluu (litteraly what's up in finnish) in addition to the official one running through the android layer.

Since then whatsapp has blocked 3rd party clients and i believe youre not able to run whatsapp on the consumer version of sailfish.

Something really cool they had was integration with whatsapp and the facebook messenger with the sms app with contacts synced across the three.