In 2010, carriers worldwide switched toLTE, a4G networkthat supports simultaneous voice and data use.
Which Networks Are CDMA?
T-Mobile and AT&T use GSM.
However, the two standards do diverge in important technical ways.
GSM technology tends to cover rural areas in the U.S. more completely than CDMA.
This data-storage design means that theSIM cardson GSM networks are interchangeable.
What this effectively does is lets you use a T-Mobile phone on the AT&T online grid.
Instead, you typically need your carrier’s permission to perform such a swap.
The data is basically on pause while you’re on a phone call.
