Mobile usage tipped passed the 3.3 billion point in November 07, with many of these users in the non-Western world. Internet Evangelism Day has a webpage about the potential of using mobile devices for evangelism and discipleship. One point they make is that radio ministries to the non-western world can draw on their big reservoir of previously-broadcast material, and where programme content is not date-sensitive, offer it as MP3 downloads, so that it can be shared virally, both through the Web, and also on to mobile phones which have MP3 capability.

http://ied.gospelcom.net/mobile-outreach.php#developing

(Thanks Tony!)