Imagine a very heavy call volume situation where agent A answers a call and the customer asks specifically to speak with agent B. If transferred the customer may will endure another long frustrating hold time. Politely advising the customer about the situation, agent A would suggest to transfer him to the voicemail of agent B instead. Agent B will return the call as soon as he is available, after hearing the message left by the customer.
Transfer to Voicemail is available both as a dial code and from the TeleConsole web interface.