How to transmit voice signal and receive on radio?
The first thing you have to know is that transmitting on the FM band is something heavily regulated. Your emitter must not exceed a specific power or range. Check the legislation of the country in which the device operates.

For this you will need an FM transmitter. You can buy them pre-made, or build them with very few parts. It might even be possible to get it to work without additional hardware and some creative hacking (some smartphones or tablets use the BCM4329 chip for example, which is capable of FM transmission).


  And what happen if i ll broadcast on same frequency on which already data is broadcasting ?


The strongest signal wins.