Hi
Read your post and just for your information this is what I have found. The Galaxy radio firmware looks at the 3G signal and the AP signal and compares them, if the 3G data signal throughput is faster than the AP data it will switch to the 3G one by default you can prove it by turning off the data on the phone and checking the connection then it will work for a time, but as soon as the signal and data rate falls below the threshold it will switch to the 3G signal by default.

I hope this makes sense to you it's a very annoying but Samsung don't seem to care about it.

Ray