You use warm transfer when you need to speak to the User prior to transferring the call. For example, if the Receptionist answers a call and needs to transfer it to John Smith (Ext 310), but first she needs to talk to him and tell him who's calling, she will use a warm transfer.
The Caller ID will show the Ext number of the user that transferred the call. For example, if the receptionist (Ext 100) warm transfer's the call to John Smith (Ext 310). John will see Ext 100 on his device.
Use blind transfer when you do not need to speak to the user first.
Use blind transfer when you need the Caller ID of the original call to show up on the user's device.
We are a financial planning firm in the U.S. When we receive a phone call, our administrator can see the caller id from a client or customer. When she transfers, internally we cannot distinguish the difference between a transfer or an internal call on the receive phone's caller id. All calls show as a direct call from the administrator on the caller id.