>That would still allow a FOSS GSM stack, it would just lead to some legal problems when trying to use a modified version in that particular regulatory environment. Better than nothing.
I don't really see a point. What use is FOSS if you are not allowed to modify it?
>Also, what do the regulations say that implies "whole software+hardware package"? A naive wording would prohibit most smartphones
Nope. Most (all?) current smartphones have a discrete GSM chip, which is controlled using a special serial interface. So licensing requirements stop at the interface between this chip and the main CPU of the smartphone.
But it's actually an interesting topic. CyanogenMod has recently been forced to pull support for Samsung Galaxy S Vibrant because of problems with 911 service (some problems with audio routing). AFAIR, it's flat out illegal to operate a phone incapable of calling 911.