Michael Washington will show you two ways to call LightSwitch methods from a Silverlight custom control.
Source: LightSwitch Help Website
It is easy to create a LightSwitch application using your own custom user interface (UI), composed entirely of Silverlight Custom Controls. The article This Is How LightSwitch Does MVVM, covers the basics of how you bind Silverlight Custom Controls to LightSwitch Properties and Collections. This article demonstrates two ways to raise LightSwitch Methods (in a normal Silverlight MVVM applications these would usually be Commands), from a Silverlight Custom Control.