The one-way audio issue is caused by the default transfer methods used by different software versions of Cisco CallManager Express and Cisco Unity Express (CUE).
CUE version 2.3.1 uses the semi-attendant method as the default transfer operation. Prior to version 2.3, CUE used the blind transferorbye-also method. Cisco CallManager Express versions earlier than 3.4 use the blind (bye-also) transfer method.
Cisco CallManager Express version 4.0 and later use the semi-attendant transfer method. Therefore, CUE 2.3.1 is not backwards compatible to any Cisco CallManager release earlier than 3.4, unless the transfer method is changed back to blind (bye-also).
The issue is documented in Cisco bug ID CSCse31911.
To resolve this issue, perform one of these procedures:
Change the Cisco IOS version on the Cisco CallManager Express to 12.4.4XC or later, so the transfer method is the same on the Cisco CallManager Express and CUE 2.3.1 systems.
Change the transfer method on the CUE to blind bye-also to allow interworking between earlier versions of Cisco CallManager Express and CUE 2.3.1.
Change the CUE configuration under the ccn subsystem sip,and issue the transfer-mode blind bye-also command.