To be fair, there are a lot of things that many people do with their GSM phones that are actually relying on the so-called "SIM menu" and other SIM features, without knowing that this is so. I can, for example, pay stuff with my "other" phone by charging my Visa card. There's a whole lot of communication going forth and back (pin codes, for example) that kind of look like SMS messages but aren't the normal ones. All this is made possible by low-level SIM card features, and they are regularly getting updated by the carrier, directly to the SIM.

I happens to know (being a technical kind of person) that this is how it works, so I use another, "regular" GSM phone with that card. In the N900 I use another card which I only use for simple calls and data transfer.

My point is that it's difficult for a regular user to know that things they take for granted in a GSM phone may rely on GSM/SIM features not currently supported by the N900.