The LM4890 is a 1 Watt Audio Power Amplifier.

Datasheet: http://www.ti.com/lit/gpn/lm4890

We chose the LM4890 because of its impressive THD and PSRR numbers. We felt that during the demo process, amplification may be needed in order to properly hear the caller on the other end of the line. The LM4890 would work together with soft control via AT command to amplify the audio output from the SIM900. diff_amp_ref