In order for the BeaglePhone to work as a phone, we needed to make sure that we added in a mic and a speaker so the user can actually talk on the phone.
We designed are circuits according to the reference diagrams that were listed in the SIM900 Hardware Design manual. For the amplifier circuit in the speaker design, we used TI’s LM4890. The diagram for the amplifier block is shown in the Parts section under TI Parts. It is repeated here for convenience.