While the application processor is an important component, it is only _one_ of many components in a smartphone. You have to think about the specification of things like the power management IC, the audio codec, the camera sensors and any other peripherals.
Oh, and talking about the OMAP: It is one of those parts that use an Imagination PowerVR GPU, which is the equivalent of nVidia in the embedded space: You cannot imagine any company that is more closed. Even as a device manufacturer, even under NDA, you will never get any bit of source code of the driver...
Most importantly, even though the 2G/2.5G/3G/3.5G baseband runs a proprietary firmware (like your wifi and bluetooth), the external interface/protocol needs to be documented.
If you look at people trying to get a truly open source software stack to work on any modern smartphone, the modem interface is where you waste months of reverse engineering, typically with very little success.
The Palm Pre is one example, where an undocumented binary protocol is used. There's a whole team looking at the binary stream going back and forth, without big success so far.