I hear that the extended battery fits under the regular door. see vid:
http://www.youtube.com/watch?v=rTbb2f81_HI
http://dealnews.com/iphone/deals/384043.html detail on how to get battery for $35 with free overnight shipping.
http://www.cellphoneshop.net/mbbach.html 8 bucks for a charger for just the battery. keep my original battery juiced up. ps cellphoneshop.net is awesome. cant say enough about the deals and fast shipping.