APRS messages can be sent by licensed ham radio operators by direct radio or direct internet connection.
If the remote users wish to use RADIO to send these APRS messages they will need to.
Become a Amateur radio Operator. I did my Ham exams through the Seven Seas Cruising Association sponsorship program. It was free to do.
Get a Amatuer Radio call sign issued.
Buy a 5-8 watt hand held VHF $50.00 Baofeng is fine.
Possibly you will need a simple home made Yagi antenna to increase range.
Get the free APRSdroid app for android phone off the APRSdroid website.
Connect the android earphone out cable into the Handheld radio microphone in connector.
Tune Radio to the desired APRS frequency.
Turn on VOX (Voice activation, triggering of "press to talk button".)
Create APRS message with OUTNET as the address in APRSdroid and hit send.
It will then send a modulated sound to the radio which will broadcast it out.
APRS messages have no acknowledgment or error correction.
Hopefully a APRS I-Gate or digi-repeater on the ground or in space will receive it and get it into the APRS network and forward it to OUTNET.