If you have upgraded your Windows Phone to version 8.1 (and you should if you are a Windows Phone developer) then you will have found out about Cortana. She is the Windows Phone equivalent of Siri, with one or two significant improvements on the genre. Snag is, she is only available to Windows Phone users in the USA at the moment.
The good news is that you can get Cortana goodness on your phone from anywhere in the world, just by setting your region and language to USA. The bad news is that this stops you from being able to buy things from the Windows Phone Marketplace (although you can still get updates to installed programs).
However, there is a workaround for this if you happen to have a second Windows Phone. Leave that in your home region and then use it for all your purchases and you will then be able to "re-install" them on your Cortana enabled, USA region, device.
Update: Actually I think it might be even easier than this. Remember that you can buy applications and games for your phone via the Windows Phone website.