I've seen a few examples on file upload from WP7 - there a good answer here to upload a file. But in my case I'm sending the file to a 3rd party who expects from form fields with the POST. I haven't seen any examples of this yet.
There's a codeproject article here, that explains how to do it in non-silverlight friendly code.
I could port over the codeproject article - or does this already exist somewhere?