The AppointmentExtensions class in the Telerik.Windows.Controls.ScheduleView namespace provides you with a number of useful extension methods for working with appointments. Here's a list of them:
GetOccurrences(this IAppointment appointment, DateTime from, DateTime to): Gets the occurances of an appointment for a given interval.
GetOccurrencesWithoutExceptionsFromDateTimeRange(this IAppointment appointment, DateTime from, DateTime to): Gets the occurances of an appointment for a given interval without the exceptions from the recurrence rule.
IsAllDay(this IAppointment appointment): Determines whether the specified appointment is an all-day appointment.
source, IDateSpan span): Returns a collection of occurrences from a set of appointments for a given interval with all exceptions from the recurrence rule. The final collection of occurences is sorted by their Start property.