PARIS, FRANCE: "Dongle" may sound a bit goofy, but the innocent-seeming technology is emerging as one of the biggest challenges to the mobile telecoms industry in coming years.

Alongside smartphones, these 3G cards or sticks that allow people to get online via the mobile network from anywhere have come to symbolize how a goldmine of surging data traffic risks becoming a nightmare for mobile operators.

Dongles are often sold with a flat-rate data plan, or with a subscription allowing a certain number of megabits of data to be used. They are fuelling a boom in mobile data traffic that is so heavy it is putting unprecedented stress on networks.

Yet even as traffic explodes, revenues from these new services aren't keeping up because of the intense pressure on prices -- so investment in improvements risks squeezing margins.

"Mobile broadband is manna from heaven for consumers, but it is hell for operators," said John Strand, who has consulted for global mobile operators for more than 12 years.

As more people access the internet over mobile phone networks using laptops with 3G cards, Apple's iPhone or Research in Motion's BlackBerry, data traffic is doubling every six months globally and growing even more rapidly in some countries.

On the day pop star Michael Jackson died, data traffic on Australian telecom operator Telstra's network jumped 170 percent.

"Everyone wanted to know what was going on at the same time," said Mike Wright, Telstra's director of wireless engineering. "It put an enormous stress on the system."

A laptop equipped with a dongle consumes 450 times more bandwidth than a classic mobile phone, said Pierre-Alain Allemand, who oversees the mobile network at France's second largest operator SFR.

Yet competition is so intense, few operators increase rates.

The situation is putting mobile operators from India to Sweden in a bind: they have to invest heavily in their networks to prevent congestion and outages, yet doing so risks hurting their long-term profitability.

Many have taken to rationing bandwidth by slowing down the traffic of the heaviest users.