[jwise0]

That's not always the case. For instance, on Galaxy Nexus (CDMA), the radio is split from the AP, and are in fact manufactured by two completely different folks (the AP is TI OMAP, and the radio is VIA Telecom). I'd imagine the same thing with Mediatek, who is a large and growing player. You are right that Qualcomm does fuse their radio with their AP, though, and they do control quite a lot of the US market.

[sounds]

Well, good, if the radio and baseband do not live on-die with the AP. Market forces are pushing for a completely integrated design, but it's interesting from a security perspective.

The baseband is still considered the master CPU during boot - at least on the CDMA Nexus. So although there are some corner cases in terms of architecture, the security model is still completely broken. Send a payload to the baseband over the air, compromise it, and the entire phone is yours.

[akgerber]

Qualcomm mostly has the modem on the same chip as the apps processor, but not always: the recently-popular APQ8064[0] (used in the Nexus 4) had a separate modem.

[0]http://en.wikipedia.org/wiki/Snapdragon_%28system_on_chip%29