It's not really the matter of free software, it's the matter of trying to
execute your freedoms that licenses like GPL want to protect.
To use a GSM/UMTS/LTE/etc. baseband device on public network, without special
permissions, it has to be certified. This certification happens on
hardware+software combo - so if you change anything in software of your
certified modem, the certification is automatically revoked and you're not
allowed to legally use such device on public networks anymore until you get
it certified again.
It's not US specific, in Europe it's very similar, if not the same.
Even if we could build such modem by ourselves (but most likely we couldn't -
it's very hard to get it right, much harder than building the whole
smartphone with ready GSM module), all we could do to make it "free" would be
to release the sources used to build a blob you would get with the device.
That's not enough to call it fully, legally free in my book.
Of course there are also some illegal projects - you may want to browse
Openmoko mailling lists for "FreeCalypso" project, which is illegally using
leaked sources for Calypso firmware to build free modem that is fully
functional as a phone (OsmocomBB is not, and they don't even aim at it - it's
mostly research project)
BTW, you might be interested in this interesting conversation that happened
few hours ago on #qi-hardware channel:
http://en.qi-hardware.com/irclogs/qi-hardware_2013-11-01.log.html
DocScrutinizer05 is the author of the Neo900 idea - he's that ex-Openmoko
engineer I mentioned earlier.
