calling wcf service with parameter from silverlight4

Question

I write WCF as follows

namespace EventViewer.Web
{
    [ServiceContract(Namespace = "")]
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
    public class EventVwrService
    {
        [OperationContract]
        public IEnumerable<string> GetFieldValues(FieldType field)
        {
            switch (field)
            {
                case FieldType.Source:
                    return new List<string>() { "SQL Server", "BizTalk Server", "MSIInstaller", "ADV", "SQLAgent" };
                case FieldType.EventId:
                    return new List<string>() { "10115", "20988", "23434", "12323", "890099" };                        
                default:
                    throw new Exception ("Unknown type");
            }
        }
    }
}

I have to call WCf according to combobox selectied items.

Please help me