Sometimes, when the phone is not picked, the caller is automatically redirected to the voice mail. That means that when someone calls you, he or she will hear some dial tones before going to the voice mail where they could record their message. In Verizon, you can actually set the number of rings before voicemail.
In this case, the agent shows concern for the customer and wants to serve him in the best possible manner. The agent is also polite and courteous.

Hello! You have reached the voicemail of John Doe . Please leave your name, phone number, and a brief message and she will return your call as soon as possible. Thank you and have a great day.
You might also consider giving them the option to skip your voicemail message completely by pressing another key (again, check with IT). You also want to make callers aware what you will return their call, instead of telling them that you will try to return their call--and let them know when you are likely to do it, if possible. If necessary, provide additional or emergency information in your voicemail greetings. My dentist, for example, lists his cell phone number for emergencies.