All of this assumes you are in the US.
My understanding of the associated FCC rules is: You cannot modify or create an FRS, GMRS or MURS radio without going through FCC certification (legally, Part 95 rules). You can create up to 10 ISM band transmitters (Part 15 rules) for research and development or experimentation as long as the transmitters meet the FCC technical requirements for part 15 ISM transmitters. This means you can use parts like the AT86RF212 (which is available in modules) and an audio codec like G.711, G.729 (now patent free) or SILK/OPUS to convert the analog audio to a digital stream. G.711 can be implemented on any microcontroller, G.729 or SILK generally require an ARM running at 72Mhz (or equivalent in other processors like the PIC32s).
Using a codec and a digital transmitter is a little more difficult but much more interesting from a project perspective. You can also transmit data including GPS, inertial sensor data, biometric data, etc. If you do go with the AT86RF212 or a module using that chip, you can expect most of a mile @ 100Kbps (line of sight) or several miles @ 40kbps or with an external power amp.
If you want to experiment, take a look at the FreakDuino 900Mhz boards. You will only be able to do G.711 with the processor on that board but you can get started really quickly. G.711 required 64Kbps, do you'll need to run at least 100kbps for your on-air data rate. The board also has an RF power amp, and the two boards I have did meet FCC rules for part 15.