We are a .Net shop that has standardized on WCF Services. We are in the processs of developing an iPhone application that needs to make secure web services calls to obtain d
I agree with Yaron Naveh's solution too, probably the best bet is to use SSL. I believe SSL/TLS encryption is better performance wise than message/XML based encryption in WCF too.
I think the certificate would probably need to be from a trusted CA (certificate authority) for this to work though. From memory, I had difficulty with the iPhone SDK with self-signed certificates, but that may well have changed in the last year...