Android will need to grow past iPhone in sales before it can start to catch up in installed base (just as the Nokia installed base is probably still higher than iPhone right now), but due to market growth I'd give it a couple of quarters once you pass in sales.
This trajectory hardly supports the "people only buy Android because iPhone isn't on Verizon" theory.
Some Australian stats for Q3 last year provided by IDC: http://www.idc.com/about/viewpressrelease.jsp?containerId=pr...
It seems to be roughly mimicking the US situation except lagged by a quarter and with Nokia switching places with Rim as the fading leader.
Also, I liked this quote from the guy at IDC "It's looking like next year it's going to be close between Android and Apple but I would be inclined to say that Apple will keep its lead, although we have been under pretty much every quarter with our Android forecast so anything really is possible at this stage," said Novosel. "Given the way that it is growing, this time next year Android could be number one."