nice project idea..
I recommend you to use pic18f452. It has 8 bit adc. Use a carbon mic. Put adc in continuous mode and you will get sampled values of analog voice signals in the adc register. Send each sample value to the serial port, where you can use a simple rf module like tws434 (ask or fsk). The baud rate should be less than 3000.
At the receiver end use a rws434 and connect the data pin to the serial port. write the serially received 8 bit value to any output port for 8 pins, which are connected to 8 bit dac. If everything works fine, you will get the transmitted voice at the output of dac.
Complex coding and circuitary required. All the best..