We have a customer with two UC500s in a multiple site configuration. We are not using VPN - it is a MPLS configuration with a Windstream SIP trunk.
When a outside call comes in over the SIP trunk and a user transfers the call locally at that site, the user receiving the transferred call can see the caller ID from the original (outside) caller once the transfer is complete. However, if the user receiving the outside call transfers it to a user at the other site, the receiving user only sees the internal extension of the senders phone even when the transfer is completed.
Any thoughts on this?
Can you make sure that it's configured on both UC500's?
voice service voice
Also make sure that you don't have "no remote-party-id" configured under sip-ua for both UC500's as well.
If it still doesn't work can you attach the 'show run' from both UC500's and include the 'debug ccsip message' output when you do the transfer operation?