questionshow windows phone (8) switches between wifi and…

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Not exactly an answer to the question, but ...
... if you were still using the Android phone, you would not have this issue. I've learned to avoid Windows for phone, just because the design focus is rarely on the user experience, more about top down, you-get-what-we-give-you, be happy.

(Oh, not that it matters, but the networks (WiFi vs cell carrier) are supposed to be prioritized with rules, usually the faster connection preferred. But there should be an option to make one the preferred or default, with the alternate the fallback/rollover. Make sure the Win8 UMA is enabled? http://en.wikipedia.org/wiki/Generic_Access_Network)

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@tpscan: Glad you started off with "Not exactly an answer....."
However I do appreciate the included link, that's something new for me.