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?