Mobile phone users are increasingly signing up to more than one account as new data shows that users of mobile services number fewer than 2.3 billion, against total mobile subscriptions of three billion worldwide.

The latest data from Informa Telecoms & Media shows that subscription growth is being driven by the expansion of networks in developing markets and by more people choosing to own a second or third subscription.

The analyst firm predicts that users of mobile services will not reach three billion until the end of 2009, by which time subscriptions are forecast to reach four billion.

Informa recorded approximately 1.32 subscriptions for every mobile subscriber worldwide at the end of 2006, meaning that that around one in four subscriptions is a second or third subscription.

"The number of multiple Sim users is expected to continue to rise as operators seek to extract incremental revenues by offering second Sims for cheaper call rates, particular data services, roaming etc," the report stated.

"Even in western Europe, where multiple Sim ownership has propelled the mobile penetration rate past 100 per cent, subscriptions continue to increase."

As revenue spreads across more subscriptions, and as mobile telephony extends to more people on low incomes in developing markets, average revenue per user continues 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.