Wifi calling uses your internet connection to route just the the call, not SMS or MMS (thanks Sprint....). VoLTE uses the carrier's LTE data connection to route the call and allows for SMS and MMS at the same time. When on a wifi call, you can still receive SMS and MMS but not if you have a shit cell signal (doesn't even matter if you are on a call or not, with a shit signal you will still have trouble anyway). The Pebble is used to boost your cell signal so your SMS and MMS will be more reliable (and your LTE data connection). For actual internet use, you are correct, you can just use your wifi.
Femtocell for the Home
For the consumer, Femtocells can be used to transform an already existing internet connection into useable cellular service. It may sound counter-intuitive, but there are many people in the United States who have access to high-speed broadband but who are unable to make phone calls from anywhere inside their home, and for people facing that situation, femtocell technology may be their best option.
Here’s why: Femtocells operate like a tiny cellular base station, literally tiny, at about the size of a cordless phone’s base station, and can be easily attached to your home internet network modem. The Femtocell then transforms your home broadband connection into a usable cellular signal that can be used to make phone calls and send and receive SMS text messages.
In a scenario like this, a femtocell system may be the absolute best option, especially for consumers who are unable to utilize Wi-Fi calling with their current contacts and cellular provider. Most individuals, especially those who run a small business from their home, still require a reliable cellular signal in order to handle their affairs, and a Femtocell network can provide 5 bar connectivity from anywhere within the home.
Unfortunately, this cellular connectivity does come at a cost. Because the Femtocell uses the existing broadband to create the cellular signal, there can be a noticeable loss of broadband speed in certain situations where phone calls and web browsing (especially uploading or downloading) behavior is occurring simultaneously. However, if your home office broadband connection is currently 50 Mbps or faster, then your internet connection should remain perfectly steady, even if you decide to use both at the same time.