I'm trying to find a way to mimic the behavior of stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding
from the iPhone, using C# (for Windows Phone).
I don't know anything about iPhone programming, and a web search for that doesn't seem to provide any document pages that might explain what it actually does to help me figure out how to mimic it. I mean, I can see that it "percent escapes" a string using an encoding, but I can't find any examples of what it does to confirm that the output I would be getting is correct. Is it just a simple URL Encode?
I'm not pretty sure if I understood your question, but HttpUtility.UrlEncode might be what you're looking for. At MSDN you'll find it's definition and examples.
Update: this is the official doc from Apple, regarding the iOS method you mentioned.