IP phones are physical office phones that make use of Voice over IP. It connects the phone service through the existing internet infrastructure, by using an Ethernet cable. IP phones include cordless phones, conference phones and desk phones which resemble a lot like a traditional.
T.38 is a protocol that explains how fax can be sent over a computer data network. It is required because fax data cannot be transmitted over the Internet in the same way as that of voice communications. The fax messages are sent as TCP/IP or UDP packets.
The interesting thing about VoIP is that the user can choose to place calls in multiple different ways: an IP Phone, a softphone and the one and only, an ATA.