I posted this on another thread (my own, actually), but there's an app called "Fetch" (actually, it looks like they renamed it to "Fetch My MMS") that takes care of the logging into VMM for you. I grabbed it and love it so far.
It doesn't fix viewmymessage's instability, but it's a lot easier to use, and even organizes your downloaded messages.
http://phase2games.com/fetch