First, in /etc/services, at this line:

fastagi         4573/tcp                        # Asterisk AGI



Second, create /etc/xnetd.d/fastagi with:

# default: off
# description: fastagi is a remote AGI interface
service fastagi
{
        socket_type  = stream
        user         = root
        group        = nobody
        server       = <path to phpagi-fastagi.php>
        wait         = no
        protocol     = tcp
        bind         = 127.0.0.1
        disable      = no
}

Make sure you set the path to the phpagi-fastagi.php script.  Set the user
and group to a non-root user if none of your scripts need root access. You
might consider using posix_setuid and friends to reduce privileges. Change
the bind address to your outbound IP address or to 0.0.0.0 to allow anyone
to connect. Be sure to read up about xinetd and take advantage of security
features it provides.  Fast AGI doesn't provide authentification.  It's up
to you to keep unwanted visitors from extracting information from your AGI
implementation.


Third, write your code.

Take special notice of how fastagi.php works:

	1. $fastagi is initialized as a new AGI.
	2. The script determines which script was requested.
	3. The script is called using
	   reqire_once($fastagi->request['agi_request']).
	4. Your script takes over.  You must not create a new AGI, but
	   insead use the $fastagi instance that has already been created.

In your dialplan:

exten => 5551212, 1, Agi(agi://127.0.0.1/myscript.php)