Hello cuong hoang,
Tasks such as scanning and faxing require access to local PC resources. Unfortunately the Silverlight plugin and its browser hosted nature will not allow this.
The platform lacks a printing support also . However here you have some chances. You can use the hosting browser printing support to provide some limited printing capabilities. For example our RadGridView uses such technique to provide the PrintToHTML() functionality.
So in general implementing these in Silverlight with the current version is kind of impossible. You may use external - non Silverlight components (e.g. ActiveX ) . You can provide some communication between your SL application and these external components via the HTML bridge provided by the platform.
Still you have to thing about security as such approach would require explicitly allowing browser to access local resources.
In conclusion I would highly recommend to use WPF instead of Silverlight for such projects. There you have a powerful printing and text management, the whole .NET framework behind and a lots of ways to interface devices such as fax machines, modems, scanners etc.
the Telerik team