If you do a lot of traveling for business or pleasure or your business requires you to deal with several currencies at a time, a currency converter application on your Windows Phone 6.x device can come in handy when you need to do a quick conversion or just to check the foreign exchange rate.
Mobile Currency Converter is a free application using a Sense-like interface that allows you to convert to and from over 150 worldwide currencies also displaying the exchange rate at that certain moment based on information provided by Yahoo! Finance so it’s rather accurate. As far as installation is concerned, download the CAB to your device and install it. Make sure you have .NET Compact Framework 3.5 installed as it’s a prerequisite for the application to properly run.
Source: XDA Developers