Using an on-site PBX means you own the hardware of your phone system. You can modify the system to you exacting specifications, including changing phone numbers and adding extensions as necessary. You will also be in charge of ensuring the security of your data stores such as phone number listings and voicemail recordings.
Company Description: UniTel Voice is a cloud-based virtual phone system priced and designed for startups and small business owners. When it comes to affordability, features, call quality, ease-of-use, or customer support, UniTel Voice has you covered.

Business professionals are also encouraged to keep their voicemail organized. Delete any messages from the office phone that are no longer necessary after calls are returned, and write down any phone numbers that are needed at the time the message is listened to. If modern voicemail service is utilized, such as that supplied by Voicemail Office, in which voicemail and fax messages are received in a staff member’s email inbox, the individual should write a short explanation in the body of the email if forwarding any voicemail messages to other staff members.
Assessing the number and quality of features available can also staggering. We assumed you'll want the basics of call forwarding, voice mail boxes, and a standard menu that lets customers select where they want to direct their calls. But consider other features, like applications that will allow portability from business to cell phone, features that will translate voicemail to text or email, call recording, fax services, and even features that will work with Google documents, Salesforce, or your office software. How much of these additional features does your company really need, and how much are they worth to you?