It should be something like this:
function callcenter($func,$value,$position)
{
}
Where $func is the function to be called,
$value is the parameter for $func,
and $position stands for index of $value,
for example,
callcenter('func',1,2)
should actually call func(null,1)
callcenter('func',1,3)
should actually call func(null,null,1).
Say,leaving other positions as null.