You can't take a unlocked GSM phone onto Verizon or Sprint. You can't take a Verizon phone onto Sprint. You can't take a Sprint phone onto Verizon.
The only carrier you can choose with GSM is T-Mobile. But wait, they use the 1900MHz 3G band, so if you've got a phone that doesn't use that band, you're stuck with EDGE data.
LTE won't change this, they've chosen different bands.
The only carrier you can choose with GSM is T-Mobile. But wait, they use the 1900MHz 3G band, so if you've got a phone that doesn't use that band, you're stuck with EDGE data.
LTE won't change this, they've chosen different bands.