Yesterday, Adam Kalsey and I talked about his experience with changing mobile phone carriers when purchasing the Motorola MPx200. In the article, I speculated that the SIM card issued by his previous mobile carrier may not be compatible with AT&T Wireless:
Another issue may be that the SIM card issued by his previous carrier may not have worked at all on AT&T Wireless. I know people who have had to change SIM cards to stay on the same carrier after switching from one city to another due to a move.
My conclusion is that SIM cards may look the same, but not necessarily posess the same features. Operation Gadget readers, feel free to correct me if I’m wrong.
Last night, I started looking for more information about inter-carrier SIM card compatibility, to see if any end-users had done research into this kind of problem. It turns out that people who do a lot of travelling to Europe and Asia want to buy pay-as-you-go local mobile service, but they run into problems because their mobile phone handsets are often locked by the carrier from which they originally purchased the handset.
Schuyler Erle wrote a helpful article for the O’Reilly Network called Unlocking Your Nokia Mobile Phone that explains the undocumented procedure for unlocking some Nokia GSM handsets so that that they will accept SIM cards from any carrier. He was able to use the procedures discussed in this article to unlock a Nokia 3650.
So, it’s clear that SIM cards from different GSM mobile carriers are compatible with all GSM handsets. The problem is that the handset manufacturers provide their mobile phone carrier customers with an ability to lock handsets so that other carriers’ SIM cards are not accepted. This lock-in technique not only prevents users from taking their handsets with them to another carrier if they choose, but it also makes it impossible to use pay-as-you-go services while travelling overseas. This is a bad deal for customers, and we should have the option of unlocking our phones at any time, unless it is specifically prohibited in our service agreements.