Outwardly, you might not even tell the difference between a VoIP phone and another business desk phone. VoIP phones tend to have handsets, receivers, speaker locations, and button placements that make them physically indistinguishable from the business phones you currently employ.
VoIP phones use the same keypad as landline phones. The keypad comes with nine numbers, zero, and corresponding letters that enable alphanumeric input. If you've ever used a phone before, you've seen this keypad.
VoIP phones generally have dedicated buttons for redial, transfer, conference, hold, mute, voicemail, and speaker phone. These buttons are set along the side of the number pad. VoIP phones and other business phones use these features almost universally. That said, VoIP phones are capable of HD Voice, while other business phones are not.
HD Voice offers at least twice the audio range of landline phone service. The spread for landline voice quality is 3.4 kHz (3400 Hz), but the spread for HD voice is 7 kHz (7000 Hz). In other words, the quality of your calls will be much higher using two VoIP phones than two traditional phones.
Many VoIP phones also support Power over Ethernet (PoE), which allows you to power the phone through a PoE switch instead of a power adapter. This reduces clutter on your desk and simplifies inventory management. It can also save you money, as power adapters are often sold separately from the phones.