I\'m architecting a .NET \"web service\" and an iPhone application that will consume these services. I\'m curious if there are any best practices for architecting the protocol
Check out this blog post for a quick overview on how to create a WCF service for your iphone app.
I know RemObjects SDK for OS X
I hope it can be helpful for you.
We're currently using a WCF based REST/POX service for one of our applications. I would recommend sticking with REST/POX as there are no class generators for web services (that i know of) on the iPhone like you get in the .NET world by adding a service reference. This will make the parsing a lot simpler as you wont have to worry about all the extra junk soap adds to the messages.
Basically take a look at NSUrlConnection and NSXmlParser and read up on "Key Value Coding" (makes the xml parsing a LOT easier) and you'll have everything you need to get it done with a minimal amount of code.