While most cellular phones will work on St John, only AT&T and Sprint have no roaming charges in the US Virgin Islands. But, many of the beaches look directly at the British Virgin Islands and often you will pick up their signals, so we recommend turning off your phone or at least putting it in airport mode while you are at any of the US National Park beaches on the north shore.
Since the recovery after the 2017 hurricane season, we’ve noticed that Verizon has gotten better and Sprint has gotten worse.