So, sim card, depending on model, has only fiew kB of memory in them, and holds only fiew things in that memory:

  • phone number

  • uniq id, so carriers can identify you

  • pin number

  • sms/contacts

  • temporary data for carrier, etc..

Source: https://en.m.wikipedia.org/wiki/Subscriber_identity_module

Any phone, that you can now buy, supports multiple frequencies, that it can send data through..

If this is true, does sim card has any say in what type of network speed you can use? And if so, then why?

Co's, as far as I understand, it's phone that has to be 4g ready, or 3g ready, not the sim.. you must have 4g plan from our carrier, ofc, but it's only matter of carrier plan..

I'm seeing so many articles saying that sim card must be "4g ready".. But I fail to find any info on why would a sim card have any impact on the matter..

Hope someone will be able to explain this to me.. (sources would be appreciated)

  • I don't exactly know the answer but the SIM has an area to hold network specific data. Usually this is what's updated when you first get a SIM and you get a 'network update' message. This will tell the network what services you are subscribed to so in theory this is all that's needed to access 3G, 4G etc. However maybe there are differences in the memory on the SIM between older SIMs and newer, and to store the data for 3G & 4G it needs a new card. – tjmoore Aug 9 '15 at 10:13
  • Thanks for answer.. To bad I can't find 100% source for this.. – ExClouds Aug 9 '15 at 10:22

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