Quote from: theymos on December 03, 2010, 02:17:16 AM

That would be a really efficient way of downloading the block chain, especially for poor communities. You can use Bitcoin with even the most primitive dial-up connection if you can get the block chain.

It's probably possible to allow people to download a "block digest" containing the first few few bytes of all addresses in that block. This wouldn't work with non-standard transactions, but it should allow general use without downloading entire blocks. Even this might be too much data for super poor communities in Africa, though.

http://www.wmo.int/pages/prog/www/TEM/EMDCS-INT/satbroadcast-india.htm

If this page is remotely recent, then datacasting a daily digest of the most recent blocks would be relatively cheap for all of Africa, India or South America. A company that sold POS devices for businesses without any reasonable broadband access to the Internet could sign up for the daily digest, receive their gear & a blockchain on a thumbdrive, and then be kept up to date withing a day by the daily digest. At $10 per megabyte (per continent, presumedly) that's expensive broadband, but not if shared across 1000+ subscribers. Even at twice that price it wouldn't be out of sorts for this kind of thing. Granted, those vendors wouldn't be able to prevent a double spend, but if we were talking low value trades, such protection might be unnecessary. Those same subscribers then might be able to charge a small fee to individual bitcoin device users for access to their blockchain, thus keeping local devices up to date with just a wifi connection.