See Buying Kindle books for the iPhone in Australia - a success story
. So far as I know, what works from Australia will work from anywhere outside the US. Note that a small percentage of Kindle ebooks are in the TOPAZ format, but most are AZW which is functionally identical to MOBI and the DRM can be stripped using mobidedrm. The ebooks are downloaded to your iPhone (iPod Touch) and must be uploaded from there to a PC (say) if you want to move them to another device.