Actually I'm not sure I'm experiencing the same issue you are describing but this is the only result on Google for 'CdrRGSCallList'. For me, the stored procedure was taking so long to execute when using the transferred calls flag (@_CallType = 4) that
it was completely unusable.
After doing some further digging into the stored procedure it seems like the transferred calls report worked but only for a very small time period, passing in a period of 1hr54m work returned results within 16 seconds, however passing in a time period of
1hr55m took several minutes to execute. If you pass in an even longer period the time taken to execute took exponentially longer, so long that SSRS times out whilst trying to generate the report.
Anyway, I added two missing indexes that the execution plan recommended adding and now it executes in <1 second.
CREATE NONCLUSTERED INDEX [IX_CdrRGSUsage_MissingIX] ON [dbo].[SessionDetails]
(
[ReplacesDialogIdTime] ASC,
[ReplacesDialogIdSeq] ASC,
[MediaTypes] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
CREATE NONCLUSTERED INDEX [IX_CdrRGSUsage_MissingIX2] ON [dbo].[SessionDetails]
(
[CorrelationId] ASC,
[MediaTypes] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
Hope this helps somebody.