mobile not-quite-me

i like the idea of apple’s mobileme, but i wonder if it will be possible to use external addresses with it. they say: “With MobileMe Mail, you can create an email address that’s personal and easy to remember. Maybe it’s yourname@me.com or maybe it’s something clever. Whatever you think up, it will be your best email address yet.”

my best email address yet is the one that is portable to other services. my mac.com address is totally useless, since i never saw enough value to .mac and it no longer works.