Something like a 3DR radio + Raspberry Pi + speaker + MAVProxy would give you a quick and cheap solution to this.
If you're wanting to scale it down further, perhaps a 3DR radio + small Arduino + text-to-speech chip would work.
In terms of sorting out the verbal messages, check out the source code of Mission Planner, APM Planner or MAVProxy - they've all got text-to-speech functionality for the telemetry from an APM.
If you haven't seen it already, check out:
It's a very small, cheap and neat solution that kind of achieves the same thing, except it converts mavlink to frsky. The advantage is that its runs over the existing 2.4ghz rc link and displays and speaks the data through your tx which is incredibly convenient while you're flying, much better than having to plug a usb dongle into a tablet and hold it separately. 3dr has done a very similar thing with the new solo controller.