On the ThinkPHP blog today, there's a new post that demonstrates their experience with the API of the spreadshirt.net website (a t-shirt/item printing site).
I just came across an old entry of the Exciting Ecommerce blog (German) which tells that Spreadshirt.net, one of Germany's hottest Internet startups, has a SOAP interface. spreadshirt.net itself seems to be developed in PHP, and so I started my IDE and played a bit with it.
They include an example of the call to the API using the built in SOAP functionality for PHP5. It makes a basic connection and pulls down some articles.