[Q] Stock non-branded i9100 can't see Sprint or Verizon in USA? topic

I've got a stock, un-branded European i9100 with a Vodafone SIM card in it. I come to the USA, turn on WCDMA, and still don't see Sprint, Verizon, or any of the many other networks that Americans complain about so much. For that matter, it doesn't see T-Mobile either. Why can't I roam onto these networks? I'm not in a remote area -- San Francisco Peninsula.