Unfortunately, AT&T's outer packaging of the 1520 is very sparse on details. The only info printed is general package contents (i.e. "Nokia Lumia 1520, USB charger", etc...), AT&T's "4-Star Eco-Rating", and some legal copyrights. Even the screen size isn't listed on the box.
However, Nokia U.S.'s specifications page for the AT&T 1520 shows the supported bands as:
Data Network
.LTE network bands: 2, 4, 5, 7, 17.
.LTE max data speed DL: 150 Mbps .
.LTE max data speed UL: 50 Mbps .
.WCDMA network: 850 MHz, 900 MHz, 1900 MHz, 2100 MHz.
.WCDMA max data speed DL: HSDPA - 21.1 Mbps .
.WCDMA max data speed UL: HSUPA - 5.76 Mbps .
.GSM network: 850 MHz, 900 MHz, 1800 MHz, 1900 MHz.
.GSM max data speed DL: EGPRS 236.8 kbps .
.GSM max data speed UL: EGPRS 236.8 kbps