No longer will you need to stay close to your analog desk phone to receive customer calls, or communicate with a colleague. You have the freedom to roam. As long as you have a working internet connection, you can communicate with customers. IP phone systems allow you to take business calls from your smartphone when you’re on the go.
However, for many businesses, there's a need to route calls to the PSTN and other analog phones. This may mean a PSTN gateway, or even a hybrid PBX, where there's at least a small telephone switch located at your office. Your VoIP vendor will let you know if this is necessary at the planning stage. Note that these days, a PBX looks exactly like the other servers in your data center, except with an attached means of handling local and analog phones.

One thing to remember is that it’s not all about you. Yes, you need to recognize what makes your life easier, but you need to make sure you know what makes your customers’ lives more difficult in order for you to determine what kind of actionable voicemail greeting you need them to hear. This, of course, will make your life easier too.
Voicemails need to maintain a professional consistency that’s aligned with the entity it’s representing. That said, the structure can vary depending on the situation. There’s no template set in stone. In fact, trite and generic should be off the table. The goal should be a balance of uniqueness and practicality.