Before you can start considering a brand, you need to figure out exactly how you want your business to use a phone system. Look at your existing phone system and decide whether you're going to simply keep all of it and bolt some VoIP functionality on top, retain only part of it, or replace the whole thing. Frequently, a total replacement isn't in the cards if only because some parts of your existing phone system can't be easily changed over to softphones or even desktop VoIP handsets.
Optimum is the first landline telephone service provider in the U.S. to launch High Definition calling. HD calling is the next generation of voice technology that gives you less background noise, sharper sound quality and increased clarity in your phone conversations. To experience HD calling, customers and call recipients must subscribe to Optimum Voice and use HD-capable handsets.

But it can also handle other functions, including session setup (initiating a call at the target endpoint—the phone you're calling), presence management (giving an indicator of whether a user is "available," "away," etc.), location management (target registration), call monitoring, and more. Despite all that capability, SIP is simple compared to other VoIP protocols primarily because it's text-based and built on an easy request/response model that's similar in many ways to both HTTP and SMTP. Yet, it's still capable of handling the most complex operations performed by business-grade PBXes.
The most professional voicemail message should include a formal tone and specific instructions. For example, you may say “Hello, you’ve reached [your name], [job title] at [business name]. I’m sorry to have missed your call. Please leave your name, contact information, and reason for calling so I can get back to you promptly.”