Andaman and Nicobar Islands are group of small islands in Bay of Bengal. Major tourist places include Port Blair and Havelock islands where have 4 mobile providers currently active.
1.) Bsnl 2g + 3G
2.) Vodafone 2G only
3.) Airtel 2g only
4.)Reliance cdma 1x .
While most local use Bsnl only for better 2G coverage as 3G signals are almost non existent and even is you find one speed is very low as everything go via satellite uplinks becoz Andaman and Nicobar islands is yet to get a subsea cable.
Out of other three operators Vodafone has best coverage at 900MHz (remember Andaman comes in WB telecom circle) while Airtel is 1800mhz so little lower and rcom has cdma coverage only. I think Idea subscribers roam on vodafone network. Not sure about which network Tata docomo and rcom gsm roam on not sure if they even provide roaming service here.
Network Present in Andaman islands
Bsnl 2g 900mhz + 3g 2100mhz
Vodafone 2g 900mhz
Airtel 2g 1800mhz
Reliance 4G 800/850mhz
Jio is also available andaman nicobar islands.