Da Voismart Knowledge Base.

SetCDRUserField(value): Set the CDR 'user field' to value
       The Call Data Record (CDR) user field is an extra field you
       can use for data not stored anywhere else in the record.
       CDR records can be used for billing or storing other arbitrary data
       (I.E. telephone survey responses)
       Also see AppendCDRUserField().

This application is deprecated in favor of Set(CDR(userfield)=...)