Read this
Stack Overflow question. While the official standard for HTTP says that there should be no maximum, in reality there are maximums. IE 8 and IE 9 have an upper bound of 2083 characters. All browsers have
some limit. I would say that Windows Phone has a similar limit to IE 8 and 9.
You could try forming the HTTP query yourself and send it via a TCP socket.
The other way of thinking about it is that any URL that long is broken.