"SmsComposeTask" is a sealed class present in the "Microsoft.Phone.Tasks" namespace and contains two properties called "Body" and "To". You can set the phone number in "To" field where you want to send the sms. Set the message in the "Body" field before you call the Show() method to launch the messaging application. Both the fields are optional. Once the application launched in the UI, user can set those manually in any case.