Is Wi-Fi always favoured over other data connections?

Question

I am at home and I would like to be sure that the data connection is always going through the Wi-Fi rather than the (expensive) data connection.

Is it enough to simply turn on Wi-Fi and connect to the (password protected) network? How can I control that the download is happening through the right connection? Can sleep (or other events) disable/change/toggle this setting?

Answer 1

In Android, AFAIK, when you connect to an active Wi-Fi network, mobile data (GPRS, 3G, etc) will be disabled (even if are turned on) temporary. So it would be OK to just connect to the Wi-Fi network. But, if you want to be sure about disabling mobile data, you should go to Settings -> Wi-Fi and Networks -> Mobile Data and uncheck the option to disable mobile data. (in ICS it's in Settings -> Wireless and Networks -> More -> Mobile Networks)

Answer 2

An adition to yrajabi's anwser:

In Android, AFAIK, when you connect to an active Wi-Fi network, mobile data (GPRS, 3G, etc) will be disabled (even if are turned on) temporary. So it would be OK to just connect to the Wi-Fi network. But, if you want to be sure about disabling mobile data, you should go to Settings -> Wi-Fi and Networks -> Mobile Data and uncheck the option to disable mobile data. (in ICS it's in Settings -> Wireless and Networks -> More -> Mobile Networks)

Sleep might change this if wifi is set to sleep when screen is off - wifi turns off and data comes back on(unless data is force-disabled as per yrajabi). To keep wifi on during sleep be sure to set: Settings> Wireless & Networks> Wi-Fi settings> MENU button> Advanced> Wifi Sleep policy to Never.