- Install Termux,
 - Generate your keypair,
 - (Test connection on localhost etc.)
 - Copy your private key to your SD card in the phone,
 - Copy the key from your phone to your computer,
 - (...)
 - Connect with your Android device:
 
You can find more information on the Tilix web page [1].
ssh <phone_ip> -p 8022
Notice: Your Termux app does not have to be running in the task manager in order for you to be able to access it through SSH.
If you receive a message: "Connection refused", verify whether you selected the proper port, adding the -p 8022 parameter to the command. If you encounter a Permission denied (publickey,keyboard-interactive). error
To connect:
- Run Termux on your Android phone,
 - Find your phone IP using 
ifconfig, - Type in Termux: 
sshd, - SSH to your phone IP issuing 
ssh u0_a152@<phone_ip> -p 8022. 
SMS API
See here.