Are you a eco-green lover/supporter? If you are, then this “CallABike” concept will be a good choice to show your concern to the environment. A Germany eco-concept company, Die Bahn offers a service named “CallABike” system. This is the rental process for “CallABike”: A customer calls the company via touch-tone and he/she will be provided four-digit number to open the bike. The customer will get another verification call after the lock had opened.