SIP Phones are the same thing as VoIP Phones or Soft phones. These are telephones that use VoIP technologies for making calls over an IP Network or the traditional PSTN networks.
There are two types of SIP Phones. The first type is the hardware SIP phone, which resembles the common telephone on the outside but uses purpose built hardware inside so it can receive and make calls using the internet instead of the traditional PSTN system.
SIP Phones can also be software-based. These allow any computer to be used as a telephone by means of a headset with a microphone and/or a sound card. A broadband connection and connection to a VoIP provider or a SIP server are also required.
Read more about 3CX SIP / VoIP phone.
Read more about the different types of VoIP / SIP phones.