You prefer to use an FM walkie talkie for the transmitter and receiver, so it would be helpful to know which model of walkie talkie you prefer to use. Since we must interface to these walkie talkies, a bit more information can be had by looking up the specs for the chosen model.
When interfacing to an FM voice radio, you can choose to do so through the microphone and speaker connections, which would be the easiest, or you can choose a more complex method. If you choose to use the mic and speaker connections, say, through a headset connector on the walkie talkie, then you must learn that these connections are AC coupled and filtered to pass primarily 300Hz to 3000 Hz only. The pass band is also not particularly flat in many cases. So, if you must pass some sort of serial bitstream through this, you must run it slow enough to pass through this bandwidth, and you must ensure that there is no spectral energy below 300 Hz.
One way to avoid these complexities is to modulate your data into some sort of audio. One common and old fashioned but reliable way to do this is using DTMF tones. The idea is that the transmitter sends a pair of tones to represent a logical one and a different pair (or no tones at all) to represent a logical zero. But you are then limited to passing fairly slow data since the tone decoder must hear quite a few mSec of tone to decode them, so only tens of bps is practical. In any case, DTMF transmit and receive chips are available still.
If you have not already procured the walkie talkies, then consider a more up to date method. For example, you might consider using a zigbee transceiver pair available from Digi International (through several distributors). One model worth looking at is the XBeePro available as small pcb modules with serial port interface for approximately $20 each. These would be relatively easy to interface to the serial port of your uP. The range, however, might be disappointing since they only work over perhaps a range of 25 feet or so.