The concept of either phone is the same. It uses wireless technology to connect with a base station that is connected to the phone service to make and receive calls. The phones will likely look very similar. You would have the phone which will have a screen to see the number you are dialing, or CNAM of the incoming call. Below that maybe some function buttons or the numeric keypad with the * left of the 0 and # right of the 0. Many such phones will use a contact pin for charging the phone.
DECT phones uses 1.9Mhz frequency which is low bandwidth, but farther distance. Keep in mind with a DECT phone, you are only carrying voice so there isn’t a need for high bandwidth. DECT phones are ideal for small and medium residences. DECT phones also can be bought in sets, but the maximum I seen a base station to accept is 5. A few base stations can accept multiple lines – therefore increasing the versatility. However, I only seen these multi-line support on SIP/VOIP base stations such as with Grandstream.
A Wifi phone uses your home’s or business Wifi capability. In case one doesn’t know, Wifi has a set limit on all of the devices combined. Therefore, if you have a 1,000MB connection, and 10 devices, each device is given an allotment of 100MB. A Wifi phone will work fine in this manner as with a DECT phone line, voice doesn’t demand that much in the form of data. All Wifi phones are SIP phones. This is because the base station is your Wifi Access Point. Many Wifi phones will support one or two lines. I personally have a Wifi phone, and it supports 2 accounts, although I only have 1 account installed.