Telecommunications terminology has long been confusing, and it's getting worse. Terminology used by equipment manufacturers and service providers can be inconsistent and ambiguous. We'll try to help you understand, on this page and in other pages in this section.
All IP phones are VoIP phones.
All VoIP phones are IP phones.
All SIP phones are IP phones.
Therefore, all SIP phones are VoIP phones.
However, not all IP phones are SIP phones.
And not all VoIP phones are SIP phones.
SIP is pronounced like sip, but IP is pronounced like eye-pee.
Although SIP phones use IP (and are a type of IP phone), the "I" in SIP stands for "initiation" and the "I" in IP stands for "internet." The "S" stands for "session" and the "P" stands for "protocol."
Most telecom and data professionals pronounce VoIP as vee-oh-eye-pee, but amateurs say voyp.
Phones with HD (high definition) audio have extended frequency response for more lifelike sound -- but you should not expect anything special if the phone on the other end of the conversation is not an HD phone.
IP phones are not just for large corporations. They offer many advantages for small businesses, especially with employees working in multiple offices -- or at home.
There's more in the info sections, linked below.