There are a few recommended options, though ultimately it will depend on your personal preference after a review of each company’s benefits.
Each offer ease of use, are easily scalable, easy to transfer phone numbers to existing landlines or cell phones and are generally inexpensive for all the features they provide.
Most of the internet-based phone systems don't include any long-term contracts as well and you can get multiple numbers. One phone number for marketing - seller leads/buyers any type of leads, and one for business - Contractors, business associates, etc.
Also, check out www.whichvoip.com - a website that compares all the different voice over internet providers so you can compare the companies and see which one is best for your business.