I read this report on GigaOm and it really sent my head spinning. There are 4 billion mobile subscriptions currently according to Wireless Intelligence (owned by the GSM Association). This is scheduled to hit 5 billion by the end of this year. Talk about impressive numbers considering the last billion were added in the end of 2007 until the end of 2008!
The most interesting part in my opinion is the breakdown between GSM, CDMA, and WCDMA. GSM owns the world with 81% of the worlds mobile subscriptions. CDMA has a marginal 10.28%, which explains why many CDMA devices come out months if not years after their GSM variants.