@philip 16Mhz band 3, 10Mhz band 1 is available in Kerala for auction.
vil is having surplus amount of spectrum in your circle (Kerala)
12 mhz of band 8,
19.8Mhz band 3,
20Mhz band 41,
10Mhz band 40,
10Mhz band 1 in your circle.
I think they will trade excess spectrum with Airtel in future.
Here TN, except jio no other network have sub ghz spectrum for 4G.
Spectrum holding of Airtel looks same for TN and Kerala in terms of 4G.
And most importantly some amount of spectrum is expiring in 2021 for Airtel, vil especially 2G spectrum. And 3.75Mhz of band 5 is expiring for Jio in 2021.