but for that to work, you need to attach an antenna, no? and where do i get such an FM transmitter? AND android does not support it in the software level, and there's no protocol for the waves?
Regarding the 'protocol for the waves,' you'll need to play with modulation. That’s the fun part. In technical literature, there are many well-defined modulations (like AFSK or FSK) with clear suggested applications for low-SNR environments.
As for Android support, I have no idea. I understand that in this thread, 'free' sounds like 'freedom,' but freedom has a cost. The freedom of communication requires investment: in hardware, software, and the time to learn the physics of the environment.
because the fun thing is cool, but people want some usable...
If the requirement is to communicate where consumer standards like Bluetooth fail, like in a ship, you have to choose the system for the environment. I evaluate these choices like an architect building a robust system, rather than just using what is available at the nearby shop.