1. A method for preserving stable calls during failover, comprising: during a dialog between two user endpoints, determining whether a standby call processor has become operational, the standby call processor becoming operational when a corresponding primary call processor is in fault; receiving a signaling protocol message from a requester after the standby call processor becomes operational; determining whether the signaling protocol message includes an in-dialog signaling protocol request; responsive to determining that the signaling protocol message includes the in-dialog signaling protocol request, determining whether a call state associated with the dialog is found in memory; and responsive to determining that the call state associated with the dialog is not found in memory, returning a non-call terminating error response in response to the in-dialog signaling protocol request, the non-call terminating error response causing the requester to terminate the in-dialog signaling protocol request without terminating the dialog.