As a customer service agent, what do you use to keep track of customer information such as phone number, e-mail, etc.?

In Customer Service agent also a perform as a customer relationship agent also. it is always necessary to update all information of the customer from his contact no. to his service history. if customer generate a  query about the service you should know about the customer before visiting to him if possible share all this detail to all your team member. By this activity the trust of customer will be grate on your Company or Brand

The above information (such information), I think it is better if the client will provide himself during love (think no one like if during intercourse found out that you own such information without his knowledge)

As a customer service agent I would ask my customer to fill a form which will allow them to enter all the details of the customers. Then I would use the computerised system to record their information to use it as and when required.