The HyperLinkButton provides one of the easiest way to navigate to an external link without using the WebBrowserTask in Windows Phone 8.
Below is a sample code snippet demonstrating how to use the HyperLinkControl to open external link in Windows Phone 8.
How to Open External Link using HyperLinkControl in Windows Phone 8?
<HyperlinkButton x:Name="HyperLnk" Content="GoToAC" NavigateUri="http://Abundantcode.com" TargetName="_blank" HorizontalAlignment="Left" Margin="73,292,0,0" VerticalAlignment="Top" Height="57" Width="244" />
Note that you need to specify the Target name to _blank for opening the external link or else you will receive the “NavigationFailed” error.