i use my 8120 for internet and UMA calling.

There are a couple of things to note.

If you want to use wifi instead of data then you have to be connected to a wifi spot - always check in manage connections that you have a green tick next to wifi otherwise you are using your carriers network.

If you go to options > mobile network and mess with the 'connection preference' then you will be changing how CALLS are made from your phone and not how it connects to the internet. This has nothing to do with the internet on your phone unless you set the phone to wifi only. In which case you have disabled yourphone from the carrier.

If you want to make calls via wifi or more importantly UMA then you need to be able to login toa wifi router. before you can make or receive calls via UMA you have to find the router. This is a feature useful for those who work or live in bad signal areas for their carrier.

If you want your browser to only use wifi then you have to set it to hotspot browser otherwise it will connect via the first/best available network. In my case when I get to work or comehome it finds my wifi. Out and about on the street it uses the carrier.