Users often don’t invest enough time into their messages, resulting in incomplete, unprofessional, or otherwise under-whelming greetings. Sure, crafting a greeting doesn’t sound all that complicated; however, there are a number of pitfalls users can fall into—i.e. informality, terseness, sincerity, lack of direction, and more. While none of these sound too catastrophic, they are often interrelated. As such, they tend to worsen any problem. For example, humor can cause informality, worsen ambiguity, and weaken sincerity. That being said, users should strive to avoid ALL these pitfalls.
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.

Does your organization have a witty catchphrase or slogan? If so, use that to your advantage. Here is one that could be tailored towards a custom software company:
The voicemail greeting is an important element of your business’ phone system because it is often the first impression of your business that customers will have. Creating a really good voicemail greeting is a unique opportunity that you can use to impress customers by putting your best face on, while increasing the chances that you’ll retain their business in those times when you can’t