This week, T-Mobile continued on its rampage to break all the rules we've ever come to know about mobile carriers, this time with a move that throws the need for a 4G network all but out the window. The big reveal? Wi-Fi calling on all new T-Mobile smartphones, a feature that will make roaming workaround apps like Viber largely irrelevant. This comes on the heels of Apple's iPhone 6 debut, which also included Wi-Fi calling as a standard feature.

The implication for travelers is huge. First and foremost, it signals an enormous change in the way we think about roaming and international phone charges (already, the carrier has made data roaming and music streaming abroad worries of the past).

But travelers who are vacationing domestically stand to benefit as well, given that Wi-Fi networks will offer better and more reliable service in many places too remote for LTE coverage. In general, this should also result in fewer dropped calls as well.

With Apple and T-Mobile on the nascent Wi-Fi calling bandwagon, there's enormous pressure on AT&T and Verizon. As for the implications for the business model of carriers worldwide--that's a whole other story.

Nikki Ekstein is an Assistant Editor at Travel + Leisure and part of the Trip Doctor news team. Find her on Twitter at @nikkiekstein.

Photo courtesy of T-Mobile US