The communication is biderectional, it can go from the Arduino to the Android device and vice versa. When you start the application, it is ready to be sent and received in ASCII mode. The data received is stored in a buffer and then will appear on the screen, there is no real-time display.
After stablishing the communication in both ways, I decided to obtain real data from real world, so I decided to measure the temperature of my workroom.
I connected a thermistor to one of the Analog input pin in the arduino and using the data it obtains I am able to read them in my Andorid device through the audio port. The speed of communication I get is around 315 bps, it is not to much, but for the moment it is enough for the data I'm testing. In a future I will try to increase the amount of data I can send.