Avoid background noise. Whether you have music playing in your office, or you’re sitting in a coffee shop, background noise can make it difficult for your customers to understand your greeting. Limit the noise around you when you leave your voicemail greeting.
The best text-to-speech voices don't sound robotic at all. Do a "text to speech" search in Google to explore your options. Type in your script and presto! You'll get an instant greeting with a natural sounding voice. You can select from a broad spectrum of male & female voices with any local or foreign accent you choose. LinkedPhone offers text-to-speech built right into our software. It's super popular and our users love it!

“Good afternoon. You have reached the office of [your name]. I will be out of the office beginning on [date] and will be returning on [date]. Please leave a brief message with your contact information, and I’ll be sure to get back to you as soon as I return on [date]. If this is an emergency or you need to speak with someone before I return, please contact [name of colleague/supervisor], [their job title], at [their phone number].”
Hope you’ve picked up some of the above mentioned voicemail greetings for your answering machine. Try to be respectful and considerate on the voicemail, such attributes lets the caller know that he/she is important and you would return their call soon.