Despite the fact that there are currently somewhere between three and four versions of Android out and running in the wild, it looks like Google hasn't dropped pace of development and is testing version 2.2 of the mobile OS, codenamed FroYo.

The firmware's browsing traces have started to be seen in sites' traffic reports, with Android 2.2 popping up across the Web. While these IDs can be easily faked, it's being seen widely enough that it seems likely that it represents testing of the update, which is expected to be launched at the Google I/O conference on 19 May.

In terms of features, the update promises mostly background tweaks and bug fixes, but does include the ability to flash the trackball on the Nexus One different colours and support for Flash Player 10.1. It'll also enable support for FM radio. Google says there are still "plenty of secrets" left in the Nexus One, so it's entirely possible that there's more surprises to be had.

But does this mean that the Nexus One is going to get 2.2 before the HTC Hero rises above 1.5? It's looking that way. At this rate, perhaps Google should just lend HTC some engineers to get the update out of the door...