The above two words are magic. If you use it more times, you get more smiles, you get more customers, more friends.

When dealing with customers, welcome them with a smile and a Good Morning/ Good Afternoon/Good Evening/Namaste! They will be happy, they will feel they are welcome. It is the starting point. And deal with them cordially and ensure that their requirements are met to the maximum possible.
When the transaction is over,  a Thank You will be suitable.
The staff of Air India, State Bank, LIC and other PSUs are practising this courtsey very effectively. Whenever such courtsies are offered to me, I feel elated and that I am welcome. This will be true to most people.
There is nothing to lose by offering Greetings with a Smile; but a lot to gain for you and your organisation.
I know that most BSNL employees are already practicing the above. Let others also start this welcome habit.
Thank you my friends!