It'll show the phone as having the 900MHz band open, from what I understand, but this has been disabled via hardware, not software, from AT&T. You can find a lot of information about this if you search the web. There's a great resource for this phone on another site, but out of respect for this site, I won't post it. It's not hard to find, just Google your phone. Anyway, don't be fooled into thinking that your MPx200 can truly become tri-band via firmware flash. Sorry for the bad news.