Vo IP phones can be simple software-based softphones or purpose-built hardware devices that appear much like an ordinary telephone or a cordless phone.
Traditional PSTN phones are used as Vo IP phones with analog telephone adapters (ATA).
A Vo IP phone or application may have many features an analog phone doesn't support, such as e-mail-like IDs for contacts that may be easier to remember than names or phone numbers, or easy sharing of contact lists among multiple accounts.
Generally the features of Vo IP phones follow those of Skype and other PC-based phone services, which have richer feature sets but (because they rely on mainstream operating systems' IP support) latency-related audio problems.
The components of a Vo IP telephone consist of the hardware and software components.