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I have a SIMCom SIM808 2G GSM module on a custom PCB based upon the Adafruit FONA. I got a bunch of 2G SIM cards from Aeris.net. The problem is when I first put the SIM cards in my device, I get "Registration Denied" (+CREG: 3) and the device will never register with the network. My AT commands and responses look like this;

AT

OK

SMS Ready
AT+CREG=1

OK

+CREG: 3

+CREG: 2

+CREG: 0

+CREG: 2

+CREG: 0

+CREG: 2

+CREG: 0
[and on and on for hours...]

Now if I take that same SIM and insert it in an old Samsung Galaxy S5, turn it on and wait a few minutes for the cellular bars to appear, then take the SIM out and put it back in my device, it registers with the network immediately and forever after. It looks like this:

AT

OK

SMS Ready
AT+CREG=1

OK

+CREG: 5

It appears that the Android phone is doing some magic to the SIM card or my account that makes the SIM card work in my SIM808. Aeris support can't see the device attempting to register.

What's going on here? What does it take to first register this SIM card from my SIM808? It not going to be possible to first put each card in an Android phone before using with the SIM808.

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    \$\begingroup\$ I don't see why this question is being closed. Could someone explain to me where the line between "use" and "design" is? E.g. does programming a micro-controller also count as "use"? \$\endgroup\$ – Dmitry Grigoryev Jun 25 '18 at 6:54
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I got some help from an Aeris engineer with this one.

It turns out that when a SIM first registers with the network, it requires better signal quality than subsequent registrations. When the SIM has successfully registered with the network the first time, some information is stored on the SIM that allows it to register easier the next time.

Mobile phones have highly integrated radios that allow them to dynamically adjust the antenna gain as needed. The reason my Android phone could do the first registration and the SIM808 could not, is likely because the Android phone was maxing out it's antenna gain and therefore was receiving the network signal better than the more primitive antenna on the SIM808

To prove this to myself, I spent some time on cellmapper.net and found out where the T-Mobile 2G tower is in my town. After driving close to it, I was able to register a brand new SIM the first time with my SIM808

I also had this same behavior with a hologram.io SIM

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  • \$\begingroup\$ Thanks for posting this up. I'm getting into a cellular module for the first time, and wondering about the SIM cards. \$\endgroup\$ – Leroy105 Nov 22 at 21:30

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