During the recent Mobile World Congress I had the chance to speak with some product managers of Munich-based Giesecke & Devrient (G&D), one of the major SIM card manufactures worldwide and for sure one topic was the Micro SIM which Apple brought to our attention when it announced that the upcoming Apple iPad will come with a Micro SIM card slot instead of a Mini SIM or ISO SIM card slot. So what's all the ISO, Mini and Micro SIM is about? When GSM hit the market in 1992, the GSM MoU also made the use of SIM cards (Subscriber Identity Module) mandatory for GSM phones. Basically, there were two SIM cards specified: The ISO SIM and the Mini SIM, also often called Plug-in SIM.
The ISO SIM card is the same size as a credit card (85.60 mm × 53.98 mm × 0.76 mm). But at this time it was already clear that smaller devices will hit the market which cleared the way for the Mini SIM card. The Mini SIM card has the same thickness as the ISO SIM but their length and width are reduced (25 mm × 15 mm). However, and this was important in terms of compatibility, the Mini SIM has the same contact arrangement as the ISO SIM and until today Mini SIM cards are normally supplied within a ISO card carrier. This arrangement allows for such a card as supplied to be used in a device requiring a full-size card, or for a device reqiring a Mini SIM card, suitable scorings manufactured along the outline of the Mini SIM card allow it to be cleanly broken out by hand:
However, even smaller devices (such as phone watches) have prompted the development of a smaller card size which was the birth of the so called Micro SIM (officially called 3FF - which stands for 3rd Form Factor). Micro SIM cards have the same thickness and contact arrangement again, but the length and width are further reduced (15 mm × 12 mm). The specifications for the 3FF or Micro SIM also include additional functionality beyond changing the physical card size:
SIM operating systems come in two main types: Native and Java Card. Native SIMs are based on proprietary, vendor specific software whereas the Java Cards are based on standards. Java Card allows the SIM to contain programs that are hardware independent and interoperable.
SIM cards store network specific information used to authenticate and identify subscribers on the Network. The most important of these are the ICC-ID, IMSI, Authentication Key (Ki), Local Area Identity (LAI) and Operator-Specific Emergency Number. The SIM also stores other carrier specific data such as the SMSC (Short Message Service Center) number, Service Provider Name (SPN), Service Dialing Numbers (SDN), Advice-Of-Charge parameters and Value Added Service (VAS) applications (all this is specified in the GSM 11.11). Furthermore, each SIM is internationally identified by its ICC-ID. ICC-IDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalization. Last but not least, SIM cards are identified on their individual operator networks by holding a unique IMSI. Mobile operators connect mobile phone calls and communicate with their SIM cards using their IMSI.
As shown above, there's no real difference between a ISO, Mini or Micro SIM card (except the technical enhancements the Micro SIM comes with but it's quite unlikely that Apple's iPad will take any benefit from it). Old-timers might remember, when they used a Mini SIM in a ISO SIM card device, using an adapter and technically there's no real reason to use of the Micro SIM for the Apple iPad (especially because the iPad is a fairly big device which should have space for a Mini SIM, unlike watch mobile phones).
Nevertheless, Apple's announcement to feature the Micro SIM for its iPad (and maybe we might see it used with the iPhone 4 as well - who knows today) generated quite an interest in the Micro SIM card. Bellow some examples from G&D how the Micro SIM might be distributed in future:
According to Giesecke & Devrient, a fairly large amount of carriers started to order the Micro SIM, now where it is used in a most likely popular device. So far, only a handful carriers where interested in the Micro SIM but this changed dramatically with Apple's iPad announcement.
Last but not least it should also mentioned here, that there's a fourth "SIM card" available on the market: The embedded SIM which is nevertheless only used in M2M (Machine to Machine) devices today - not for consumer devices.
Cheers ~ Arne