A 4G network is undoubtedly the next step in mobile connectivity at the moment, with the LTE system leading the way. While predecessor 3G was fast, 4G is faster — and in the rapidly changing tech world, things always have to get faster (or smaller), or they risk falling behind.

For AT&T and Verizon, two of the nation’s biggest mobile carriers with a combined 70 percent share of the market, falling to the back of the pack is not an option. That is the reason both companies have been earnestly pushing forward with the development of their 4G networks. Verizon touts its web as the nation’s fastest 4G network, while AT&T claims it has the biggest 4G network.

What’s not to love? Consumers benefit from enhanced networks that let them use their smart gadgets at faster speeds and in more places, while carriers enjoy the new customers who join in so they can get 4G before others. However, there is a cautionary story to pay attention to: the Korean market has shown that new customers may not be making up for all the infrastructure expenses…

Korea’s consumers on 4G networks have more than quintupled the monthly data consumption of 3G users on average. As a result, carriers see an average increase of $13 per user. While that’s good money to be taking in, the money going out to build up the 4G network might be a bit too much.

Korea’s biggest and second biggest mobile network operators have been struggling to make money off 4G for about year and a half now. The faster demand for it grows, the more investment carriers have to put into it, and the longer it takes to see a profit.

While the winds of fortune may blow differently for AT&T, Verizon, and other U.S. carriers implementing 4G — perhaps consumers here will cave in to higher premiums — the struggle in Korea cannot be ignored.

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