I am using my iPhone application on my iPhone 3G OS 3.0.1 without any problems. The application connects to an API URL at https://api.serverdensity.com/1.0/ and all requests
It looks like everything checks out with the installation of the certificate. All of the Intermediate certificates are being sent by the server: http://www.sslshopper.com/ssl-checker.html?hostname=api.serverdensity.com