Can you give more information on the FCC approval process? What requires approval exactly? If people designed open-source hardware plans, then made the hardware, then shipped it, at what point is FCC approval necessary?
A more serious problem is trying to get all the relevant firmware and radio software stack without tripping over IP that is (a) patented and (b) will only be licensed to you under NDA. Qualcomm are particularly bad at this. So you need to choose a suitable SoC with favourable IP licensing.
Writing your own "baseband" is a substantial piece of work; some people have embarked on it at http://bb.osmocom.org/trac/
Canonical's approach is sound here and their costs are realistic. Getting it done for free by people working in their spare time is very unlikely to happen.