"My reading is that modem is connected to the CPU via USB. The only other project I know of that was looking at doing such a thing were the OpenMoko guys (GTA04 with an OMAP3xxx, I think? My memory is fuzzy on this)."
First, modem connected via USB is a good thing - it's the least bad option with regard to closed basebands.
Second, it's not that rare of a configuration - I believe there are quite a few consumer smartphones that connect the baseband via a USB interface ... it's not like there's a little USB connector inside there...
"So this is essentially a small tablet running Linux with an integrated cellular modem."
I don't think that's exactly correct ...
It is indeed possible to stick a USB cellular modem onto a tablet device and even use it for telephony. The problem with this arrangement is that there are many other things (like echo cancellation and other voice enhancements that need realtime processing) the baseband processor does - and you lose those functions.
An integrated USB modem that is actually the integrated baseband of a mobile phone does not have those problems - even though the bus used is USB.
First, modem connected via USB is a good thing - it's the least bad option with regard to closed basebands.
Second, it's not that rare of a configuration - I believe there are quite a few consumer smartphones that connect the baseband via a USB interface ... it's not like there's a little USB connector inside there...
"So this is essentially a small tablet running Linux with an integrated cellular modem."
I don't think that's exactly correct ...
It is indeed possible to stick a USB cellular modem onto a tablet device and even use it for telephony. The problem with this arrangement is that there are many other things (like echo cancellation and other voice enhancements that need realtime processing) the baseband processor does - and you lose those functions.
An integrated USB modem that is actually the integrated baseband of a mobile phone does not have those problems - even though the bus used is USB.