It's not a new achievement using wifi as Telemetry but this UART to WiFi module has really long range (up to 400 meters), and unbeatable price. Very small form factor (about 2cm x 1.5cm) and light (3 gr). Great for the small sized UAVs. And your Smart Phone or Tablet will become a GCS with no additional hardware. And with module's available GPIOs it's functionality can be increased (PWM, I2C sensors) you can drive LEDs or get sensor data over wifi.
Check out eriksl's great firmware for ESP8266 https://github.com/eriksl/esp8266-universal-io-bridge
I've been experimenting with new ESP8266 UART to WiFi module and happy to announce you that it can be used as Telemetry module. It should work on all MAVlink devices that uses Serial communication. I tested with ESP-03 and APM 2.6 (3.2) and range is acceptable for Follow Me, or Guided missions. it works reliable enough (there is a still rare disconnect issue, it can be power or firmware issue -more testing needed-) , and its really cheap, start as low as 2,5 $ at several stores (its a 3.3v device you will need a good (about 300ma) power source). You should consider it as proof of concept, there is a known bug (as 3.2.1) effects that GCS failsafe not functioning, when GCS communication is lost. I think APM 2.6 users should receive at least a one last bug fix release (several reports indicates 3.2.1 has some issues with altitude calculations), of course you can compile your own verison.
For those who are interested, I can provide APM:Copter 3.2 (not 3.2.1) firmware with the fix. I am happy with it, doing some great auto flights, checking parameters, follow me flights, you can fly your UAV even without RC controller, directly from your wifi enabled GCS.