There is a sticky at the top of this forum that describes the latest OS for the 8703, including directions for installing it and user comments on results. The 8703e is mentioned as being upgraded successfully by some users, but others seem to have had problems. Best to read it and come to your own conclusions. Upgrading an OS is not hard, but it is not trivial either and mistakes can result in an inop phone. You can almost always recover, but you shouldn't attempt it unless you're comfortable with the process.
