Authorities on Monday dealt a blow to the scam-phone-call industry by busting three alleged perpetrators in New York, but they’re facing an uphill battle against the billions of calls Americans receive each year from overseas.

The feds in June announced a nationwide crackdown on telescammers when they took out 94 schemes originating from within the United States — wiping out an estimated 3 billion annoying calls, according to the Federal Trade Commission.

But that was just a “drop in the bucket,” because so many of the calls originate from outside of the country, FTC Consumer Protection Bureau Director Andrew Smith said at the time.

Scams from the Philippines, Mexico and India, outside US jurisdiction, are harder to thwart, he said.

Phone scams are easy to operate and extremely lucrative — and also difficult to trace, Alex Quilici, CEO of robocall-blocking service YouMail, told the Miami Herald in June.

“There are call centers all over the map — from Florida to Guatemala to Nigeria to New Delhi to Philadelphia,” Quilici told the Herald.

“Or just get four friends together in your apartment with a laptop and make millions of calls for nothing.”

New York City residents are among the most besieged by irritating calls in the country, according to YouMail — receiving 147 million last month alone, just behind Dallas at 178 million and Atlanta at 187 million.