The Serial Position Effect states that the human brain is most adept at recalling the first and last items in a series. For sales reps, this psychological phenomenon means that your voicemails are much more likely to be remembered if they're listened to at the beginning or the end of the day.
2. “Hi! We’re glad you called [company name]. We’re happy to help but we are either on the line with another client or on the go! Please let us know your name, number, and reason for your call today. As soon as we become available, we will call you right back. Thanks!” Ask your callers to leave a short message so you can determine when to return their call.

This point is more or less an extension of the point above. If you want to avoid sounding awkward and long-winded, you need to know what you're going to say — every good sales voicemail is conducted with confidence and definitive intention. The key to delivering on both is having well-prepared, personalized voicemail messaging at your disposal.
If you do this two or three times in a row, you further degrade your chances of ever connecting with this prospect. Since they've now seen your number come up multiple times without once receiving a voicemail, they're aware this call is definitely not one they need to take. You can bet the next time you call, they're not picking up.