PHP has a built-in SoapClient, which works quite well for SOAP requests. SOAP is a protocol that can be used to do remote method calls, for example to request address information from Webservices.nl.
As most webservices give a fairly quick response, the user does not have to wait very long for the application to react. However, this may become different when the SOAP webservice fails. For example, if the webserver serving the WSDL is down, the SoapClient constructor will block for a minute and only then throw a SoapFault. This article will explain common problems and how to reduce the annoyance to the user.