Kolkata, the City of Joy always has a sweet spot for Indian telecom. Back in 1995 Kolkata became first city to get mobile services in India, that was MobileNet from Modi Telstra - turned Hutch later, and now operates as Vodafone Idea.
Interestingly 3G, the next of 2G obviously, was not first launched in Kolkata, rather it was Delhi to get country's first 3G mobility from MTNL in 2008. And see what happens - in 8 years (however private players didn't able to launch 3G until 2010 when 3G auction did happen; so to be precise it's just 6 years) 3G is turning to be obsolete in favour of 4G (Jio was launched in 2016).
4G again fell in love with Kolkata, as Airtel became first Indian operator to launch 4G in April 10, 2012. Fyi, I attended that inauguration press meet. 4G has a very slow uptake until Jio started their commercial services in September 2016.
What I want to say, with out Kolkata touch, 3G failed while 2G is surviving and 4G is rocking. Same for CDMA too, Reliance Mobile India went for countrywide launch back in 2002 and in 2018 all CDMA networks are defunct.
Now while we are embracing 4G - thanks to Jio for bringing down the tariff to a super affordable level, Kolkata touches a new milestone as per OpenSignal's data. It's the only city in India to cross more than 90% 4G availability (90.7% to be precise) - keeping the other top areas of South East Asia behind, Hong Kong (90.4 per cent), Singapore (86.6 per cent), Taipei (89.8 per cent) and Kuala Lumpur (80.8 per cent) in terms of 4G coverage.
Well though it's impressive to reach a global standard, it's not acceptable that 4G is not that much fast in India. India's average speed is behind to that of Pakistan and Sri Lanka.
