An Ericsson survey shows that the number of global subscriptions to mobile phone services has passed over 5 billion. The global population is estimated at 6.9 billion.
It’s hard to estimate what 100% penetration in this industry is but there is a strong possibility for another billion accounts to be added in the next year. This estimate includes all service accounts, not individuals. As users begin to carry multiple devices (i.e. phones and iPads), the number of subscriptions could easily exceed the global population. In some countries, penetration above 100 percent is already the norm.
http://news.yahoo.com/s/ap/20100709/ap_on_hi_te/us_tec_global_phone_use