Verizon is a CDMA carrier and AT&T uses GSM. This means that although some of the bands overlap (including a few of their primary bands), some will not.
Carrier
| 4G LTE bands
| Main frequencies
|
---|
АТ&T
| 2, 4, 5, 12, 14, 17, 29, 30, 66
| 1900, 1700 abcde, 700bc
|
Verizon Wireless | 2, 4, 5, 13, 46, 48, 66
| 1900, 1700f, 700c
|
(Bold indicates a primary band)
So this potentially means that by and large the phones will work but it's possible you may experience dropouts if in an area where the phone doesn't support the band offered by the carrier. This will be rare but it can occur.