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Mobile handsets can have dual SIMs, where each SIM (usually) has a single IMSI. However it is possible for a SIM card to have dual IMSI as well, and in fact IMSI that can be "configured on it" on-the-fly by operator. The latter mechanism is used for roaming scenarios, such as for business customers, where one (fixed) IMSI will be used by your home-country operator's phone number, and the other (flexible) IMSI that could be configured to visited-country operator's phone number (with whom your operator has a specific roaming arrangement). This way people can call you on either number, and you do not have to swap SIMs. Note that this was possible even before dual-SIM phones became relatively common.

For multi-SIM, I found some answers such as this one where one answer suggests using MultiSIM API (from 3rd party), and another answer suggests using the official supported API available since Android 5.1 (API level >22) or the unsupported TelephonyManager way from this answer (which I presume works for older API levels as well). However, it is not evident if those API's work for single SIM multi IMSI as well.

Unfortunately, I am yet to lay my hands on dual-IMSI SIM card to try this out. While I am trying to procure one, can anyone who has tried confirm or share findings ?

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bdutta74
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  • Do you have a reference that a single SIM can have multiple IMSI? AFAIK SIM card can have only one IMSI. The procedure that you are descirbing is done by the foreign mobile company, by entering the visitor SIM's details into their HLR, not by assigning a second IMSI to the same SIM. – TDG Apr 16 '17 at 06:25
  • Don't have the specifications, although I did find few patent filings on the topic. However this has apparently quite common especially for M2M MVNOs. Here is one brochure that mentions it: https://www.eseye.com/wp-content/uploads/8344-Multi-IMSI-Explained-by-Eseye.pdf – bdutta74 Apr 16 '17 at 13:08
  • See this (https://www.slideshare.net/ikwe22/understanding-telecom-sim-and-usim-isim-for-lte) slide#35, i.e. the UICC cards can have multiple applications, even of same type. This means that a sing UICC card can have multiple SIM and USIM applications, each with it's unique IMSI. ETSI TS 122.101 seems to cover this. – bdutta74 Apr 16 '17 at 13:25
  • Very interesting. Thanks for the link. – TDG Apr 16 '17 at 13:52
  • What is the question? – QuickPrototype Apr 22 '17 at 19:02

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I'm not exactly sure what the question is, however a single SIM will only ever have one active imsi. Yes SIM cards can can multiple imsi's and an operator can update the imsi. However a SIM will only have ONE active IMSI.

A SIM can only have one active IMSI due to the SIM specification which says a IMSI must be stored in file ID: 

3F00 (MF) -> 7F20 -> (DF_GSM) -> 6F07 (EF_IMSI).

A device (phone/modem) will request the IMSI from this file and only this file. if they were two "active" IMSI's no device currently would know where to find that IMSI without a firmware change.

QuickPrototype
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  • Thanks for the answer, however my question assumed that multiple IMSI per SIM card could be active simultaneously, and how does this fact reflect on something like the SubscriptionManager API (API level >= 22). – bdutta74 Apr 24 '17 at 09:29
  • To my knowledge, this is impossible, do you have any reference to multiple "active" IMSIs on a card? The reason for a single active IMSI is added to my answer. – QuickPrototype Apr 24 '17 at 19:03
  • Older SIM cards were ICC. Newer SIM cards called UICC, can have multiple applications (USIM, ISIM etc.). Apparently UICC can even have multiple instances of ISIM or USIM application, each of which can have it's own IMSI. – bdutta74 May 06 '17 at 15:55
  • Yes True @icarus74, however only one application (SIM,USIM,ISIM) can be active/enabled at one time, thus only one IMSI will ever be active. – QuickPrototype May 15 '17 at 07:36
  • Thanks @QuickPrototype, for the clarification. I wasn't aware that only one application can be active at a time. – bdutta74 May 16 '17 at 04:20