Also on board this shield are a pair of 1/8″ audio jacks, perfect for connecting a microphone and headphones. Yes, you can actually make cell phone calls with your Arduino now. The real star of ...

While [Ilias Giechaskiel] was waiting for his SIM900 shield to arrive, he decided to see what he could do with an old Nokia 6310i and an Arduino ... via the headphone jack of Motorola phones.