The architecture is fine. A better explanation would be: if an incompetent operator use obsolete technology then its SIM card can be hacked. But any half-decent

The architecture is fine. A better explanation would be: if an incompetent operator use obsolete technology then its SIM card can be hacked. But any half-decent should be immune to this (there are billions of SIMs, and here it's "millions" only vulnerable). First, in a proper network the mobile device and the network mutually authenticate themselves. So the cell can't be faked. Then it's very easy for the network to filter such management SMS and only allow them from their trusted server. It's a very basic security precaution. If done, you don't depend on the SIM crypto scheme for secure SMS, but here too using DES is a joke and 3DES / AES have been available for ages. So I guess it's another sensationalistic report made to draw readers for most. As for intelligence services, they already have access for domestic operators. This could only be for foreign and loosy operators maybe.