Can you guys explain me how I can add voices like "40km
You have 2 questions I hope can be answered with one answer.
1. Can you guys explain me how I can add voices like "40kmh school zone ahead"?
Garmin provides free software for this purpose. It is called VoiceStudio. You can down load it from here:
http://www.garmin.com/us/products/ontheroad/voicestudio
2. If I download and install schoolzone POI from here, will those voices work out of the box?
I am not sure if it will work on your device, I do know that with VoiceStudio you can custom make your voices and even use your own voice.
I have done this and it is kind of fun to see unsuspecting passangers come to the realization that it is my voice on my GPS.