Ronald Raike's project is very helpful because it takes care of the tedious process of compiling Asterisk and the FreePBX framework for the Raspberry Pi architecture. This can be very time-consuming if you don't have sufficient knowledge of Asterisk, Raspberry Pi hardware, and FreePBX.

But at least we don't have to follow the initial steps of the instructions, since we already have a functioning Raspberry Pi system. We don't need everything the maintainer describes in his ReadMe file before "Insert the SD card and power up the Raspberry Pi," since our Raspberry Pi is already running. We start the installation directly with ./install from the installation directory in the Raspberry Pi's home directory. We can partially implement the recommended configuration if we haven't already done so. Otherwise, it will be a long installation with multiple reboots and repeated logins as root. Fortunately, the script continues from where it started the reboot. For me, the entire installation of Asterisk took about 2 hours.
You can then access the IP address of your Asterisk in the web browser and the actual configuration of Asterisk can begin.