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I recently bought some global 3G modules from Digi International and wanted to test one of them with the SIM card from my phone.

I was surprised when I saw the module couldn't connect to the network. So I then used a prepaid SIM card from the same carrier and it was able to connect to the network although I had to force a network reset in order to have a data connection because the module would fail to stablish it in the first try.

I contacted the support team and they told me that the problem must be in the SIM card or the carrier not allowing the module to connect. They told me I must use M2M SIM cards, not SIM cards intended for phones/tablets. I've used 2G modules from SIMCOM with any type of SIM card without any problems. This 3G module from Digi is based on the U-Blox 201 modem.

My question is, is actually a difference between M2M SIM cards and normal SIM cards? I know they have other form factors not available on normal SIM cards and they can also have extended temperature range and the carriers usually provide more tools to manage the M2M cards. But do carriers block connections of non-smartphones or non-tablet devices to their networks? Are the M2M cards treated differently by the network?

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There is no physical/electrical difference between the SIM cards. It is the economics of the network provider.

When a device connects to a cellular network it provides its IMEI (serial number of the device/modem) and IMSI ("number of the SIM card"). Each manufacturer has its range of IMEI numbers, so you can distinguish Simcom, Telit, Quectel, Samsung, Apple etc. just by looking at the serial number.

The operator can configure the network to disallow particular combinations. When your module connects, the network can see that "it is Digi" and look up the billing/plan information of the SIM card (based on IMSI) and decide - yes you can or no you can't connect. Maybe in the case of your network operator Digi products are treated as an M2M devices, while Simcom modules are not.

Many M2M devices send very little data per "daily smartphone standards", so the operator wants to squeeze as much money as possible by market segmentation.

Overall this issue is a pricing strategy.

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