exec() problem!

jkhost:/home# dpkg -i airtime_1.8.2-3_all.deb
******************************** Install Begin *********************************

Warning: exec() has been disabled for security reasons in /var/lib/airtime/install/include/AirtimeInstall.php on line 31
Must be root user.
dpkg: error processing airtime (--install):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
airtime

/home/airtime/install# php airtime-install.php

******************************** Install Begin *********************************

Warning: exec() has been disabled for security reasons in /home/airtime/install/include/AirtimeInstall.php on line 31
Must be root user.

    public static function ExitIfNotRoot()
    {
        // Need to check that we are superuser before running this.
        if(exec("whoami") != "root"){
            echo "Must be root user.\n";
            exit(1);
        }
    }