In PHP 5 you can use SoapClient on the WSDL to call the web service functions. For example:

$client = new SoapClient("some.wsdl");

and $client is now an object which has class methods as defined in some.wsdl. So if there was a method called getTime in the WSDL then you would just call:

$result = $client->getTime();

And the result of that would (obviously) be in the $result variable. You can use the __getFunctions method to return a list of all the available methods.

You can create a very simple JSON/JSONP API without libraries.

Here's a very basic example where you'd take an array of data, then JSON encode that array and returns the JSON, or JSONP, depending on the request:

$data = array();
//....do something to prepare your data....

if(isset($_GET['callback'])) {
    $callback = preg_replace("/[^A-Za-z0-9\.]/", '', $_GET['callback']);
    header("Content-type: application/javascript");
    echo $callback . "(" . json_encode($data) . ");";
}
else{
    header("Content-type: application/json");
    echo json_encode($data); //JSON
}