Posted 24 November 2012 - 07:23
Edit: Whoops forgot to add, you can view the current metric settings by opening up a command prompt and typing "route print". You should which devices are assigned which number.
Barring specific software that allows you to manage how the connections are accessed and when (I don't know of any personally for Windows), you can change the route metric and that might work.
If you go into the TCP/IP settings for your wireless adapter, then the Advanced tab you should see an option that says "Automatic Metric". If you turn that off, it gives you the option to change it. You would need to change it to a number LOWER than the 3G connection. I'm sorry but I'm not sure how to get to that setting on your 3G connection (however it might be in the same place for the 3G adapter as I've never used one). If you can change the 3G option, if it's set to the lowest number already you'll want to change it to a number higher than the Wifi adapter.
Theoretically, this is would cause Windows to choose Wifi over 3G assuming a Wifi connection is found. Hope it works for you. If you ever use a LAN, you would need to make sure your LAN card has a lower number than all of them so it would connect as soon as it finds a network over ethernet.