Ooma Office is engineered for great voice quality but you will need a high-speed Internet connection. You should have at least 256 kbps upstream and downstream for each simultaneous call during peak usage times. For example if you have eight users and you think up to three people will be on the phone at the same time during your busiest time, you would need 3 * 256 kbps = 768 kbps of upstream and downstream bandwidth.
To start the Internet connection speed test, click here.