With the Mango release Microsoft added front facing camera (FFC) as an optional hardware component. The main use case for a FFC is video calling, but up until this point there's not be an application that enables this. Tango, which was added to marketplace a few days ago, fills this gap. It allows you to make voice and video calls to other Tango users over a WiFi or 3G connection. 

Tango is not a universal video calling solution, you can only call those people who have signed up to the Tango service. On the up side Tango is cross platform, so it already has an established user base. The application automatically filters your contact list to only show those that have application installed, making it very easy to get up and running with your first video call.

Devices with a FFC include the HTC Radar and TITAN and the Samsung Focus Flash and Focus S. Tango will also work on phones without a front facing camera (as shown in picture below). The rear camera is used instead, but this obviously limits the usefulness of video calling.

In our test call (Lumia 800 on both ends) the video came through at reasonable quality, but there was a lot of feedback on the audio (which could be resolved by turning the speaker phone off). Applications like Tango tend to need to be optimised for each handsets camera and microphone arrangements for optimum performance. It's likely that the developer (TangoMe Inc.) has concentrated on those devices with a front facing camera.

Developers may be wondering how Tango have manaaged to create a video calling application within the limits of the Windows Phone and Silverlight APIs. The quick answer is they haven't - Tango is one of a number of applications (Spotify is another), that use native code (wrapped in a DLL) for some of their functionality.
   

Screenshots

Description

Tango allows you to make free phone calls and free video calls over 3G, 4G, and Wi-Fi. Make calls to any other person who has Tango installed on their smartphone, tablet or PC. Start a Tango call with just voice, and easily move into a video call when you have something to share. It’s easy to use, it’s fun, and it works.

Tango Features:
• Free calls between Windows Phone, Android and iOS phones and tablets, and PCs
• Save money with free international calls to other Tango members
• Start a phone call with Tango and switch to a video call when you have something to show by tapping the camera icon
• We automatically find the friends that already have Tango
• No log in and password - create an account in less than five seconds
• Invite your friends by Text and Email
• Simple and easy to use

More details on the Tango application page.