Time was, there were only four networks in this country. Then 3 came along and jumbled it all up. Now, with MVNs (Mobile Virtual Networks), there are more than you can shake an aerial at. And Google looks like it wants in on the action.
According to Pocket-lint, a MVN is already being trialled in Spain with Google's backing and, appropriately, the Google-branded SIM is inside a Nexus S. It's not available commercially yet - with the 'Google_es' network being used to test Google Voice.
It wouldn't be a real network - don't forget, MVNs are basically leasing agreements where companies buy airtime from the big boys then charge their own tariffs (think the likes of Virgin Mobile or Tesco.)
But this could be one to scare the established giants. Don't forget, Google is pushing Voice heavily in the States and clearly wants in on the action. And with its own operator, it could end up pitting itself against the status quo.
Then again, any MVN is always at the mercy of the network it leases airtime off but Google isn't afraid of trying things differently (just look at how the Nexus One was originally sold) so this could very well get very interesting indeed.