If you want learn about Customer Service, take an airtel connection. I am telling as far as service is concerned they are the best. Try calling them for any help, you will be totally satisfied. I never had a better experience than this with any service of any product.
I use a 999 broadband plan. I have my own wireless router. So far there has been no problem in connection in last 11 months. Even when I had problem with my wireless router setting, I called them and they fixed it for me(this was none of their responsibility becuase, wireless router is not provided by them). Sometimes I have called them at 9:00pm in the night, and the there service person always showed up by 9:30pm and patiently fixed it no matter how late it was without grumbling. And once the service is done, without fail I will receive a call from Airtel inquiring about my satisfaction on the service provided.
I am entirely happy with Airtel.
Abhishek