If Japan Prime Minister Yoshihide Suga thought the financial markets had a farewell message for him after his brief spell in office, he's right. That message is: Don't let the door hit you on the way out.

It is especially true for investors in telco stocks, which have regained nearly 1.3 trillion yen ($12 billion) in value since the news of Suga's imminent departure broke a week ago. Since September 3, KDDI's stock has increased 9.9%, NTT's by 7.9% and Sofbank Corp by 3.8%.

The wider market has also surged, encouraged by the promise of the stimulus programs proposed by the frontrunners to replace Suga. But there's no doubting the satisfaction for telecom investors in seeing the back of the man who had a very specific obsession with bringing down Japan's mobile tariffs. As many commentators have noted, it was one of the few policy positions that Suga actually embraced.

He had a point, though. When Suga took office 12 months ago, Japan's mobile charges were high by international standards. According to one much-cited international study, Tokyo's mobile tariffs were the highest among half a dozen major cities worldwide for big data plans and second highest for standard plans.

After taking office, Suga engaged in some energetic jawboning on mobile pricing. Fortunately for him, his prime ministership coincided with the arrival of Rakuten and of 5G, giving telcos reasons of their own to slash prices.

The three incumbents all introduced their own value sub-brands and carried out successive rounds of price-cutting ahead of the launch of those brands in March. A second survey in May found that Tokyo's data charges had fallen to second lowest among comparable cities, with a 20GB bundle costing 2,973 yen ($27.04).

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Telecoms and politics have always been intertwined, but it is unusual to find a political leader so identified with such a discrete piece of sub micro-economic telecom policy. The approach to regulating telecom pricing makes for an interesting contrast with Japan's two nearest neighbors.

In South Korea, the problem has been preventing price-cutting. Telcos have been fined again and again for excessive price competition and subsidies. It actually has a Telecom Subsidy Law aimed – not always successfully – at bringing subsidies under control.

In China, with just three state-owned and controlled telcos, prices were stubbornly high until 2015, when officials started demanding annual price cuts and performance improvements.

Over the period of the 2016-20 five-year plan, average prices for fixed and mobile fell 95%. The unit price for mobile data dropped from 35 yuan ($5.41) per GB in 2017 to 3.8 yuan in November 2020.

— Robert Clark, contributing editor, special to Light Reading