According to Wikipedia, there are a whopping 2.7 billion mobile phone subscribers in 2007.    

In 2006, mobile networks covered around 80% of the world’s population and coverage is expected to grow to 90% by 2010.

One of the most important, though behind-the-scenes, item in mobile phones is its SIM or Subscriber Identity Module, basically a removable smart card which stores key information identifying a mobile phone service subscriber.    

It comes in 2 standard sizes. One is the size of a credit card at 85.6 x 53.98 x 0.76 mm while the more popular mini version measures 25 x 15 x 0.76 mm.

Most SIM manufactures are also smart card manufacturers. The first smart card was developed in 1974, by independent inventor, Roland Moreno and today, smartcards are produced by companies like Iris Technologies, Gemplus International S.A which has been making smartcards since 1998 and Axalto Holding N.V.

Gemplus and Axalto merged on 2 June, 2006 to form Gemalto, which deploys the majority of the 80 million SIMs used in GSM mobile phones in North America alone.

A phone’s SIM holds personal identity information, cell phone number, phone book, text messages and other data, and it gives the phone into which it is inserted an identity.

Early SIMs had 8KB storage which was increased to 32KB and 64KB, while larger capacities range between 512KB to 512MB.

SIM operating systems come in two forms, Native and Java. The Native SIM OS requires a proprietary programming language and lacked interoperability between different SIM manufacturers, while Java Card is an open OS from Sun Microsystems, which is hardware-independent and had 96% of the overall market in 2004.

SIMs store specific information used to identify a subscriber on the network, including the Authentication Key and Local Area Identity. It also stores the SMSC (Short Message Service Centre) number, Service Provider Name (SPN), Service Dialing Numbers (SDN) and available Value-Added Services (VAS).

SIMs can be identified internationally using an International Circuit Card ID (ICCID), which is either printed or engraved into the SIM. To be identified on individual operator networks, there’s the International Mobile Subscriber Identity (IMSI), which mobile operators use to communicate with their particular SIM card or to connect calls.

Worried about people forging your SIM? In theory there’s a slim chance of this happening since each card has a unique 32-digit Ki, also stored in the network’s database called a Home Location Register.

However, in practice, cloning SIMs is a simple matter, just search Google on “SIM card cloning” for details.

For example, one site explains how it could be done using a home made SIM card reader costing US$5 connected to the serial port of your PC. Using a software like Simscan, you can read the IMSI and extract the Ki which can then be copied to another SIM.

With the cloned SIM, people can make phone calls or using other charged services at the expense of the of the original sim card holder.

Actually, cloning was generally much easier in the early 90s due to poor security but present mobile phone users don’t have to worry that much since the SIM cards themselves perform security operations on the data contained within to prevent cloning.

Now will SIMs go the way of the dodo one day? Possibly, according to The Guardian’s Victor Keegan who believes they could as more people turn to VoIP services like Skype, which charge minimal rates or make free VoIP calls over wireless broadband WiMAX, iBurst or WiFi connections, instead of expensive mobile calls. Keegan added that SIMs could later be used on prepaid packages as a fallback.

However Keegan could be wrong, as more uses are being found for SIMs.

For example, some large mobile operators are considering using multi-megabyte SIMs for instant branding of handsets, digital rights management and Internet connectivity.

Major SIM vendors are introducing multi-megabyte SIMs with 1,000 times or more capacity than their conventional counterparts, using Flash memory, like in memory cards and USB drives. Many developers have also created or are working on applications that run exclusively from SIM cards.

Orange in France began a commercial pilot trial of a 128-megabyte “SIM+” card  about two years ago and the response was encouraging and convinced Orange to extend it throughout Europe.

The card is preloaded with about 7 megabytes of video clips, posters and ring-tones, plus room for user-downloadable content. 

Only time will tell whether such an intelligent creation in the SIM card could actually die away like the dinosaurs but you now know that little bit more about the card without which your phone is useless.