The only one and one mobile operator in the world is "The Vodafone" . The mobile operator is present all over the world.
The coverage, range and service quality is excellent. The calls never gets dropped. The cost of the calls are almost very cheap. Now a days, roaming charges have been reduced in vodafone making it one of the cheapest mobile operator.
The data plan you get is also very affordable, you get unlimited 2G, 2 GB for 199 Rs for the entire month. If you want 3G, it is little expensive.
You can find vodafone with most of the IT professionals for the best coverage, cost and quality service which is offered by Vodafone.
Vodafone is slowly going to bring 4G in the coming months.