FCC approval is actually quite easy and affordable (less than 10k), as long as your equipment passes first time. The best way out is to buy a dongle or module

FCC approval is actually quite easy and affordable (less than 10k), as long as your equipment passes first time. The best way out is to buy a dongle or module from a 3rd party who has already got approval for it. If the RF module has approval then you don't have an issue. You still need a different kind of approval for your electronic device, but they are just reselling a 3rd party device so no issue there either. I haven't made a mobile phone - instead I have worked on other RF devices. Perhaps there are issues I am not aware of (a public mobile network probably has a lot of checks and balances that are much more expensive)