That's not "not clear", that's just an engineering problem. Heck every digital device on the market has a "local oscillator" many devices have multiple local oscillators. Getting a passive receiver complaint with any kind of standards is orders of magnitude easier in both requirements and solving engineering problems than a transmitting device, and even those are quite easy; case in point: every mobile phone or $30 UHF radio.
That and the fact that it's a known engineering problem with a known engineering solution which has been implemented many times before. The Galaxy S had FM, so did the S2, so did my old Saegem dumb phone, so did my not iPod, and my Sony Walkman. Oh and so does my $30 UHF radio.
It is not a problem, the only reason these devices aren't used because there's very little market for it. Heck even in my car I use Pandora via phone instead of FM. Most of commercial radio is a joke, and for the odd occasion when I do tune in I use a digital radio which gives me a far wider option for radio stations locally then the usual shit (40+ stations instead of the 10 or so local ones). FM in the phone is dead because people in general don't want it.