To check to see if your phone is compatible with US networks please find the IMEI of your phone.
Please note: AT&T doesn't always work based on the IMEI check.

See below different ways to find the IMEI of your phone:

1. Enter *#06# on your phone's dial pad.
2. Check in the setting menu:
    Android: Go to settings > About phone 
    iPhone: Go to settings > General > About
3. Check under your device's battery.
4. Look for a sticker on the box the device is from.

Please use this link to check the IMEI for compatibility.

Cellular Israel doesn't take responsibility for the accuracy of this IMEI checker.
From our experiences we have found it to be accurate for the most part.