datetime conversion and formatting used in the soap call

I would like to control the formatting of the datetime conversion used in a soap call. I have an unusual situation where an internal web service which requires 3 datetime parameters hangs when I used PHP5 to make the call to the web service. A corresponding call from VB does not hang and the only difference that I can see in the POST request is that the datetime string format is different. The PHP conversion follows the ISO_8601 standard and the VB program adds a field for milliseconds. The web service is written in .NET and publishes a WSDL. The purpose of changing the datetime conversion format is to make the request look just like the VB request (to eliminate all possible problems). -- Michael Bartz