A VPN service provider offers the users the means to get anonymous online and protects their data. They offer various packages for their users. Since this is offered online, the customers can contact at any time, literally! Here is an example of a script for a VoIP phone service for practice.
If they are calling without an expectation that you always pick up (such as if you are a business coach or a one-man shop) then thanking them for calling might make the most sense.

1.) Le hemos transferido al buzón de voz de John Doe. Actualmente, el señor Doe no puede atenderle. Si lo desea, puede llamar de nuevo más tarde o dejar un mensaje con su nombre y número de teléfono para que él mismo pueda devolverle la llamada lo antes posible.
Humor also leaves a lot of room for misinterpretation—which subsequently weakens sincerity and authority. A caller can be very turned off by merely misinterpreting your joke. Why take this risk? Additionally, this could even cause callers to question your character. Say, for example, the president of a company’s mobile phone voicemail greeting was funny. What’s to happen if the caller didn’t like or get the joke? What if they found it offensive? Another scenario is that a caller is reaching out to you for the first time—i.e. they have no idea regarding your personality. What next? The point is, with this type of greeting, humor is bound to be more divisive so just avoid it altogether. c. Poorly Pacing Your Message and Bad Time Management: Don’t speed through your message. Speak clearly so callers know what to include in their message and when to leave the message. At the same time, don’t drag your message out. No one wants to sit through a diatribe. Just get to the point clearly.