This Railfone found on some Amtrak trains uses cellular technology.

See also: List of mobile network operators

Several countries, including the UK, now have more mobile phones than people. There are over five hundred million active mobile phone accounts in China, as of 2007. Luxembourg has the highest mobile phone penetration rate in the world, at 164% in December 2001. In Hong Kong the penetration rate reached 117% of the population in September 2004. The total number of mobile phone subscribers in the world was estimated at 2.14 billion in 2005. The subscriber count reached 2.7 billion by end of 2006 according to Informa. Around 80% of the world's population enjoys mobile phone coverage as of 2006. This figure is expected to increase to 90% by the year 2010.

At present, Africa has the largest growth rate of cellular subscribers in the world, its markets expanding nearly twice as fast as Asian markets. The availability of prepaid or 'pay as you go' services, where the subscriber is not committed to a long term contract, has helped fuel this growth to a monumental scale in Africa as well as in other continents.

On a numerical basis, India is the largest growth market, adding about 6 million cell phones every month. With 156.31 million cell phones, market penetration in the country is still low at 17.45% India expects to reach 500 million subscribers by end of 2010.

All European countries and most Asian and African ones have adopted the GSM system. In other countries, such as the United States, Australia, Brazil, India, Japan, and South Korea, legislation does not require any particular standard, with the result that GSM co-exists with other standards such as CDMA and iDEN.

While some systems of payment are 'pay as you go' where conversation time is purchased and added to a phone unit via an Internet account or in shops or ATMs, other systems are more traditional ones where bills are paid by regular intervals.