A recent report published by Informa Telecoms & Media, Multiple SIMs: Quantifying the phenomenon taking mobile penetration beyond 100%, found there were approximately 1.32 subscriptions to every mobile subscriber worldwide at the end of 2006 - i.e. approximately one in four subscriptions is someone's secondary or tertiary subscription.

The number of multiple-SIM users is expected to continue to rise as operators seek to extract incremental revenues from customers by offering second SIMs for cheaper call rates, particular data services, roaming etc. Even in Western Europe, where multiple-SIM ownership has propelled the mobile penetration rate past 100%, subscriptions continue to increase.

As revenue is spread across more subscriptions and as mobile telephony is extended to more and more people on low incomes in developing markets, ARPU is continuing to fall. Expansion of the subscription base continues to offer potential for overall revenue growth, however, even as the price per minute for traditional mobile voice services declines.