Although overloading paradigm is not fully supported by PHP the same (or very similar) effect can be achieved with default parameter(s) (as somebody mentioned before).
If you define your function like this:
function f($p=0)
{
if($p)
{
//implement functionality #1 here
}
else
{
//implement functionality #2 here
}
}
When you call this function like:
f();
you'll get one functionality (#1), but if you call it with parameter like:
f(1);
you'll get another functionality (#2). That's the effect of overloading - different functionality depending on function's input parameter(s).
I know, somebody will ask now what functionality one will get if he/she calls this function as f(0).