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So far I haven't seen a cell phone that allows to detach the SIM card without first detaching the battery - the SIM card is placed behind the battery and inaccessible unless the battery is detached.

I assume there's some electrical engineering reason for that - like maybe detaching a SIM card with battery installed will damage it.

Is there any electrical engineering reason for that?

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    \$\begingroup\$ The iPhone's SIM card is accessible (and the battery is not). \$\endgroup\$
    – user3624
    Aug 10 '11 at 13:51
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    \$\begingroup\$ I can remove and insert the SIM card of my HTC Touch Diamond with the battery in place, though it's easier with the battery removed. \$\endgroup\$
    – stevenvh
    Aug 10 '11 at 17:39
  • \$\begingroup\$ Ok, I've voted to delete my answer. As either I'm totally mistaken here (Would be strange as I'm working with that stuff on a daily basis) or I've just missed the point of the question. \$\endgroup\$ Aug 10 '11 at 17:47
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    \$\begingroup\$ @Kellenjb: At the circuit level of course - system level considerations belong to mobile software design and would be offtopic here. \$\endgroup\$
    – sharptooth
    Aug 11 '11 at 4:41
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    \$\begingroup\$ @Sharptooth System level design that effects hardware is very much on-topic here. When you say "Is there any electrical engineering reason for that?" it is very hard to tell that you are talking only about the circuit level. \$\endgroup\$
    – Kellenjb
    Aug 11 '11 at 13:29
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I am currently working on a GSM connected device and I feel like I have something to contribute, although I am no expert so be sure to do further research if this doesn't satisfy.

The GSM module I am working with states something along the lines of this in its datasheet (re-worded for NDA purposes, and to make it more general):

A SIM detection pin must be used in order to comply with the 3GPP TS 11.11 document recommendation if the physical design of the mobile equipment allows the user to remove the SIM card during operation.

I combed the mentioned 3GPP document and did not find much talking about this so I am unsure of how well this is specified or if that point was from an older version of the document. Section 11.2.8 "SIM Presence Detection and Proactive Polling" of that document defines a polling procedure to detect SIM removal but only at critical times (what they call "card sessions", for example a phone call).

In any case, my theory is this: this is done as a design decision to simplify the phone firmware, as the phone would only ever need to do its SIM card initialization on power up, and to avoid having to comply with any possible procedures which only apply if you allow the user to remove the SIM card during operation. Seeing as there isn't a clear advantage of providing that feature, it's a no-brainer (for me at least) to go with a design that does not allow SIM hot-swapping.

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  • \$\begingroup\$ That was my assumption as well but I had no sources to back me up. \$\endgroup\$
    – Kellenjb
    Aug 10 '11 at 18:34
  • \$\begingroup\$ This is an insightful reason in the realm of system design, but leaves the question of potential electrical reasons open. Does anyone know if the SIM spec requires that the card survive powered insertion/removal? \$\endgroup\$ Aug 12 '11 at 14:36
  • \$\begingroup\$ @Chris Stratton, After reading some of the comments that ensued, I decided to dig deeper and I have some more info to add regarding not the SIM card spec, but the ISO 7816 smart card spec which SIM cards adhere to. I haven't had the time to but I'll update my answer when I get the chance. \$\endgroup\$
    – Jon L
    Aug 12 '11 at 16:02
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SIMs are definitely supposed to survive powered insertion and removal. They're also ESD protected so you can handle them.

Most likely it's done this way to simplify the design of the phone and reduce cost: there only has to be one access cover for the battery. This cover is the size of the battery. Therefore it covers the SIM holder, which is soldered to the board. Any other design involves extra space or another hole in the phone, through which dust and moisture can enter.

3GPP TS 11.11 doesn't say anything about batteries, but it does date from the era when SIMs could theoretically be full smartcard sized. If those were ever used they were probably removable through a card slot.

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My understanding is that at least part of the reason for this is pressure from carriers: They don't want to make it easy for users to switch SIMs, because they'd rather force you to buy more than one phone if that's something you'd do regularly.

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  • \$\begingroup\$ It is true that features are unlikely to end up on common phones without carrier interest in them or a manufacturer with some leverage to dictate their visision - dual sim phones exist, but have they ever been sold through carriers? And again, while interesting, this doesn't seem to be in the category of electrical design factors. \$\endgroup\$ Aug 12 '11 at 14:32

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