3. "Hey, this is [your name]. If you're calling for [X reason], please [contact so-and-so] or [go to our website, send me an email]. For all other inquiries, leave your name and a brief message and I'll call you back within [one, two, three] business day[s].
In an email, you may end by telling the contact what you want them to do next. In a voicemail, though, ending with something like, “Call me back,” or, “If I don’t hear from you, I’ll call next week,” can discourage the person from responding.

Depending on your connection to the person you are trying to reach, it is necessary to decide ahead of time what to say. So, avoid being the person that calls someone but then has no idea what they want to say. Especially if it goes to voicemail. Also, do not read off of a script. A simple outline can help you remember what to say, and it should flow naturally.
What you do not want to do is say your phone number so quickly that the person has to listen to your voicemail multiple times to try and figure out your phone number. We have all gotten those annoying voicemail messages where the person said their phone number so quickly that we had to listen to their message several times to figure out their phone number. Don't be that jerk who leaves their phone number so fast that the other person has to listen to your message over and over to try and figure out what your phone number is.