Interesting ... what do you actually see when you encounter a FILE type input in a form with the Pocket PC? Does it just ignore it?
The Nokia platform supports XHTML Mobile Profile, and Nokia's documentation (below) says file inputs are supposed to be supported.
However, all I see on my Nokia 3650 using its XHTML Mobile Profile browser is an editable text field -- not a file selector, so I don't know how I'm supposed to provide a path to an uploadable file. So, for the time being, I'll stick to MMS / SMTP with file attachments.
Here's the Nokia documentation (excerpt)
3.5 File Upload
The browser supports uploading content, such as images, from the device to the Web server. Content is sent from a device to the server as a Multipart Message; the server-side implementation of the content upload is similar to the HTTP upload mechanism for standard Internet browsers. The process of implementing the upload mechanism in the server side is:
An XHTML page with a <form> element is created. Inside the <form> element there are at least <input type=file> and <input type=submit> elements. The page is deployed to the Web server.
When the page is opened with the terminal browser, the user can select the content to upload.
After the content has been selected and the Submit button has been activated, the form is posted to the URL defined in the form. Selected content is part of this Multipart Message.
On the server side, the Multipart Message is parsed with an application (written with, for example, CGI, PHP, ASP, JSP, or Java Servlet) and content can be saved to the file system of the service provider's server.