WEBThis guide covers the use of the 4620, 4621, 4625, 5620 and 5621 phones on IP Office phone system. These phones are physically similar. The key difference is that the 5620 and 5621 are only supported on the IP Office where as the 4620, 4621 and 4625 are supported on a range of Avaya phone systems. The diagram below shows the main phone features: