the Plugin from the TAK Offsite that integrates with legacy radios to do basic communications in ATAK, variously called either “Hammer” or “ARIK” is now in the Play Store under the name “Hammer”. The plugin is open source, with the source of the Government’s GIT page. I anticipate that it will be resigned for subsequent versions of ATAK, though its not clear whether it will be updated with new features by the Government. If you are interested in making improvements, please contact me.
There are several other plugins that are liable to hit the play store in the next month or two.
You can find the plugin here.
Note that this video from T-Rex asked for this capability last year.