A VoIP phone is a phone specially designed for VoIP. VoIP phones are also called digital voice phones, IP phones, cloud-based phones, or internet phones, and they typically have features that make them more suitable for VoIP calling, such as better sound quality and more advanced features.
For the most seamless set-up BT recommends you use VoIP handsets.
However, you can use an adapter with your traditional handset and VoIP service.
Not all phones can be used as VoIP phones, or internet phones, but many can. In general, any phone that can connect to the internet can be used as a VoIP phone. This includes smartphones, tablets, laptops, and even some desktop computers.