WiFi calling is amazing when you do not have a strong signal indoors, below ground or so far above ground that the signal from the tower is hard to reach your smartphone's antennae. WiFi calling also helps ease network congestion by routing calls using your ISP rather than the cell tower to make your calls. It also enables networks, like T-Mobile, to offer free or very low cost calling from anywhere in the world to your home country.
A comment by milan03 on Howardforums summed it up quite nicely, technical details and all :
"In order for a wireless operator to launch "The Next Generation" WiFi Calling (VoWiFi) service that we're seeing today on devices like Apple's iPhone 6 coupled with T-Mobile, operator is required to perform the following upgrades:
1) Invest into core network infrastructure upgrade in order to provide secure AMR-WB HD Voice service over the VoWiFi bearer. ePDG is needed.
2) Launch (preferably nationwide) VoLTE service, so that the user has that seamless voice fallback to and from the VoLTE bearer.
You may ask then how's Sprint doing it on an iPhone 6. Well their backend solution isn't seamless, calls drop when you lose WiFi since they don't have VoLTE deployed anywhere. Also, early reports show that WiFi Calls on Sprint with iPhone aren't HD quality. This could be due to calls potentially being transcoded from Sprint's native EVRC-NW voice codec used on their CDMA network to industry standard AMR-WB/NB.
The real question is would Verizon be interested in any kind of compromise when it comes to voice service. The answer is most likely not.
And since they already have nationwide VoLTE fully launched, they need to implement ePDG in order to leverage this feature and do it right.
I'm not very convinced that Verizon and AT&T are in a hurry to make this kind of investment, but it would definitely benefit their subscribers."
Certainly the advantages of WiFi calling are many. T-Mobile was the first to make the leap to make it a feature on all of the phones they sell. It will only be relatively short while before you, Verizon Wireless subscribers, will get this unique and useful feature on your smartphones.
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