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Thread: what's supposed to happen when i move my SIM?

  1. #1
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    what's supposed to happen when i move my SIM?

    I got curious about this because a couple weeks ago, I got a new phone and moved the SIM from the old phone to the new one (both android phones).
    At first, I thought everything "just worked" and that is what I expected to happen, in other words, in my mind the whole identity of my service is encapuslated in the sim (I tested making and receiving a call, and I sent an SMS).
    I realized about a day later that INCOMING sms's were not being received.

    This is on Redpocket (an MVNO), in this particular case on Verizon's network.

    I online chatted with customer service and after a couple of false starts, they "reset" my account and within a couple of minutes I was again able to receive SMS (but the ones sent in the meantime seem to be lost, not that i cared); and all was good.

    Being curious, and having extra unused phones and another line, this one redpocket on ATT -- as a test I moved that SIM. Something apparently similar happened, once I moved the sim, the new phone could send SMS but not receive it. It was only a quick test, so I didn't want to or try to have customer service involved.
    I also realized another wildcard is RCS; so I turned that off to eliminate confusion.

    It all made me realize I don't understand how SMS gets routed, and who does what to whom. Is this normal? Does it have to do with the carrier's network (verizon, att, etc) or just the mvno, or something else?

    I use Google Voice as my primary number (which avoids all of these issues) but I'd still like to sometimes use and understand how the carrier-number SMS works.

  2. #2
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    what's supposed to happen when i move my SIM?

    That is not normal. Sim swaps are instant. When it comes to that. No matter the carrier. On both T-Mobile an AT&T never had that issue in the 10 years of moving sims between devices.


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    For SMS (i.e. text(no pics) sent to one person/number), sending and receiving should be instant or nearly instant. SMS uses the voice channel to send/receive. I think the network needs to 'populate' to ensure SMS receipt to new phone/IMEI. I am guessing here so no darts, please.

    For MMS (group text, text with pics), the APN needs to be configured correctly because MMS messages use data for sending/receiving. MMS will use specific servers given their content and distribution, hence the special web address for MMS in the APN. Some phones do not configure automatically.

    The above is true for traditional GSM carriers. Verizon, i believe still links numbers with devices so swapping sim cards may not provide instantaneous sms results, hence the account reset.

    Again, no darts please and if my understanding is incorrect, please educate. Hope that helps.

  4. #4
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    Depending on the phone, sometimes it requires some additional programming or configuration on the back end.

    I moved a user to a tcl 10l and initially sms/mms could not be received. They could send though. The tech support at Red pocket had to configure the account for "cdma less". Service was Verizon and previously user did not have any issues with the Umidigi phone.

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  5. #5
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    Sim swaps are instant.

    However, with the advent of RCS and iMessage, leaving those turned on when swapping the SIM to a new device could lead to the inability to receive message.

    This is especially true if switching between iOS and Android. But because both use data to route messages to apple/google servers, any device swap without turning those features off first could lead to this issue.

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  6. #6
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    Thanks for all your thoughts. I, in fact, done this without any difficulty when I got a new phone in the past but only had trouble very recently...

    I was also in the back of my mind thinking about this recently announced scheme:
    "A Hacker Got All My Texts for $16" https://www.vice.com/en/article/y3g8...kari-netnumber
    I don't mean in my case there was anything nefarious going on, but it does involve rerouting sms's,
    And as far as I can tell that scheme is independent of carrier. Which sort of confuses me.

    update: so this afternoon i (re)tried a sim swap on my redpocket/att line and all worked fine without doing anything else. so all seems well, no special action required, as many of you had stated. thx!
    Last edited by ebeighe; 04-09-2021 at 06:41 PM. Reason: Typo

  7. #7
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    Security issues like this, along with port out, SIM swap schemes are why carriers have begun pairing SIM and IMEI.

    Though there's two different kinds of pairings:

    Soft Pair - This type allows you to hot swap the SIM between devices, but if an issue arises and the IMEI does not match the one the carrier has on file, they do not have to provide any support. Not to mention that while you can SIM swap, it has come to my attention at least one carrier prohibits it in their TOS and that performing an "unauthorized SIM swap" could lead to a re-activation fee plus additional charges before they will support any issues with any devices after its noted in their system such a swap happened. (They may charge this even if you switch back to the original device if their system was able to note usage with a different IMEI.) Also with soft pair, if you SIM swap without pairing the IMEI, the carrier can decide to disable certain features (like VoLTE).

    Hard Pair - This is something that Sprint was known for with the ICCID/IMEI pairing where you cannot swap the SIMs at all. (It comes up as "Invalid SIM" in any other device and the phone will give the same error with any other SIM.) This prevents SIM swapping entirely, especially without CSRs getting involved in the process. Which is supposed to be more "secure" in that right. While Sprint was one of the primary carriers that did this, it has come to our attention some other carriers are starting to Hard Pair SIMs and IMEIs with another prime example being Tracfone. So hard pairing may become the norm in the future.

  8. #8
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    update: so this afternoon i (re)tried a sim swap on my redpocket/att line and all worked fine without doing anything else. so all seems well, no special action required, as many of you had stated. thx!

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