connecting speaker and mic to GSM SIM 900
You can use electret microphone. Connect its positive to MICP &amp; negative to MIC_N.

For speakers, I have used this type of speakers. Connections are same.

Alternatively, for testing purpose you can also use your headphone. Cut the headphone wire and you will find wires to connect with SPK_P SPK_N MIC_p MIC_N .