Windows Phone Live Tiles updating 

Windows Phone 7 Live Tile is a neat and very useful feature. To make Live Tiles live, an app needs to update its Live Tile or Tiles per its needs. For example, an email app can use its Live Tile to show the number of new messages.

There are 3 ways to update Live Tiles:

1. Microsoft Push Notification Service.  It requires a server to send updates individually to each receiving phone.  This is good for sending out message on the demand of the app's publisher.
2. ShellTileSchedule.  It is good to update a Live Tile's background image. It normally grabs an image from a remote server. This is useful if a publisher want to show certain image on all phones that have installed its app. It allows 4 intervals:EveryHour,EveryDay, EveryWeek and EveryMonth (the four values of enum UpdateInterval).
3. Background Agents.  This is the most flexible method that allows an app to update the Live Tile with an image generated in any of the numerous different ways. Its updating interval is about 30 minutes.  If an app generates a new image in the background, it should save to the folder "Shared\ShellContent\" of the isolated storage, then use ShellTile and StandardTileData to update the LiveTile with Uri("isostore:/Shared/ShellContent/ImageFileName.jpg").