You can install the play store (quick Google search and very easy to do) and then Message+. This is where I am.
However the camera on the Kindle HD 10 is so poor, I cannot scan the QR code on a standard sized smart phone to sync the Kindle. I may take it to work where I can print the QR code on Letter
We understand looking to use our application with all your devices. The Kindle HD may not be compatble with the application. You may be able to use any basic features, but not be able to sync the app with your device. Let us know if you are able to get the QR code working. We will submit your post as feedback.