Good point. But at the same time, a secure, bug free baseband won't save you from a fake cell tower that's intercepting and recording your text messages.
Yes, but a secure, bug free open baseband would, since the first use cases that would be addressed is verification of towers, not blindly camping to the strongest signal, and monitoring your cipher strength.
With an open baseband you could do much more useful and sophisticated firewalling and ACL of your interaction with the cellular network.
As it stands now, you just camp to the strongest signal and do whatever it tells you - including download and run arbitrary java apps to run on your sim card (probably without your knowledge).
