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I'm designing an embedded system that will require a cellular modem (3G). I never used one but the designs I came across with they all use a SIM card slot. I understand that this may be convenient but isn't there a way to avoid it? Why and how? What are the challenges of storing the information stored in a SIM card in any other kind of memory such as the internal memory of a microcontroller?

Thanks

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    \$\begingroup\$ Why would you want to avoid it? Other than ease of programming multiple devices how would it be of benefit to not use a sim card? \$\endgroup\$ – Voltage Spike Jan 27 '16 at 23:55
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    \$\begingroup\$ A SIM (or more specifically a UICC) is more than just some bytes of data. There's an entire engine in there. \$\endgroup\$ – Ignacio Vazquez-Abrams Jan 28 '16 at 0:09
  • \$\begingroup\$ @laptop2d one of the reasons I'm interested in getting rid of the SIM card slot would be to update over the air the SIM related data, so no manual intervention on place would be necessary. \$\endgroup\$ – rasgo Jan 28 '16 at 0:26
  • \$\begingroup\$ @msr "sim cards" are available in chip scale packages and can be soldered to your board. The sim card has memory and a crypto chip inside to prevent unauthorized access of the data stored inside. It authenticates against a private key programmed in by the network operator \$\endgroup\$ – crasic Jan 28 '16 at 1:58
  • \$\begingroup\$ @crasic, can you share some examples of those chips? Another thing is: what if I want to change the network operator of a given (m2m) device? Can I update that info (the sim card data) over-the-air? \$\endgroup\$ – rasgo Jan 28 '16 at 5:26
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The cellular modem is designed to interface with the SIM card, using the SIM card signal levels and protocols, primarily to provide cellular-phone features - i.e., ability to switch SIM cards for different users / accounts, secure identification, secure SMS storage, association of saved data to account, etc.

Because the SIM is a secure storage device, as far as I know, it is required by design, and cannot be replaced with any other storage type.

That said, it is possible to source surface-mount SIM devices (called MIM) for permanent installation instead of the 2FF or similar "cards" which require a socket. However, these are difficult to source in small quantities. But the short answer is, yes, you need one, and no, there is no way around it.

If this is a problem, then look into the other wireless services and technologies available in your area. Or consider, if you have several of these devices, could they just "RF link" to each other using any standard RF transceiver module and relay information to only one device with the desired capability? This may be far easier to implement than a creating a "cellphone from scratch."

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  • \$\begingroup\$ Thanks for the detailed explanation! A question still remains though: even if a MIM is used, is it tied to a single network operator or can it be upgraded over-the-air? I just started reading about this subject and one thing I found is that GSMA are creating chips with that feature (the "embedded SIM" has some kind of bootloader) so you can chose a network operator anytime and send that info to the embedded SIM. Not sure if these MIM also implement that. \$\endgroup\$ – rasgo Jan 28 '16 at 5:32
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A few manufacturers are now making SIM on chip parts, sometimes known as MIM (Machine Identification Modules). Have a look at http://www.gemalto.com/m2m/solutions/mim

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  • \$\begingroup\$ Thanks for sharing! Do you know if it's possible to buy these chips in prototyping quantities? \$\endgroup\$ – rasgo Jan 28 '16 at 5:28
  • \$\begingroup\$ Yes. I was offered free samples from Gemalto but decided for the moment to fit a SIM card. I understand the network operator can be changed. \$\endgroup\$ – Steve G Jan 28 '16 at 10:48

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