Though Grandstream may not be a well-known brand found in stores, you won't be disappointed in the quality and the feature-set of this system. Unlike other "small business systems" (like those from AT&T or VTech) which utilize your existing phone lines and proprietary technology to act as a business phone system right out of the box, this system will require some configuration and setup. It is a fully-functional VoIP phone system with PBX functionality (think "press one for this...two for that...", voicemail, call transfers, music on hold, connecting multiple physical locations together, etc.) If you are familiar with Asterisk and FreePBX, this system will be mostly familiar to you.
Even in today's fast-paced world, customers don't like being greeted with an automated message. According to the New York Times, callers of a certain age are put off entirely if they are answered by a voicemail instead of a real person.

Only one out of every five customers will listen to your voicemail if they don’t recognize your number. With listen rates that low, your response rates are going to be abysmal. If you have a front desk receptionist or another employee making outbound calls, you’re going to have a hard time making that worth your while.
You can’t always get to the phone when clients, partners, investors, or colleagues call you. When this happens, a professional voicemail greeting helps you make a positive impression and tells them what to do next. There are a variety of ways to convey your message. If you’re not sure what type of message to record for your own voicemail box, here’s a definitive guide to get you started.