Of course, if you are acustomer, you’ve may have had access to their on 3 application for some while, and although this works well, and performs many useful functions, it does miss out a few features that the main app features (of course, the on 3 app is free of data charges under the campaign, so should not be overlooked).
However, for those on other networks, or those wanting those few missing functions (like UK SkypeOut calls), but are happy to use up some data allowance instead, then last weekfinally released their official app. You need Android v2.1, and there’s a rather large list of compatibility issues and known issues (depending on your phone), but generally, something like the seems to have the best support.
Although it will work on either Wi-Fi or 3G connections, it will only work on Wi-Fi in the US, and head to this page to read more about the compatibility issues.
Either pick it up from the Android Market, or head to here.‘s Android page