Hi Haribabu,
You can use a DAC for playback of these voice messages. 8k samples per second will good you telephone quality sound. I assume you are not asking for music system but for process control equipment where you don't need dolby DTS or such hi fi sound stuff. 8 bit @ 8KHz might be enough. But remember even at with this sound quality for one 6 second message you will need 64KB of storage space. For storing 256 messages in plain wave table format you will need approx. 16MB of memory space. I think for message storage flash will be an ideal choice.

For recording you can use mic+amp+ADC+micro which samples a 8 bit 8000 samples per second and store the messages.

Regards,
Prahlad Purohit