mikejuk writes: Now you can add a GSM Shield to the Arduino which is about the size of a credit card and connects directly to the mobile phone system. The price is quite reasonable too, 69 euros or about $90, for an open, i.e. unlocked, phone. The card works with the usual range of Arduino boards — Uno, Mega and Leonardo — and looks very easy to interface and write code for. It connects to any GPRS/GSM network using an M10 Quectell quad band radio modem and it supports TCP/IP and HTTP over GPRS up to a speed of 85.6kbps. The card needs a SIM to work but the one supplied by Telefonica in the box has some interesting features. It only allows you to send data and SMS messages, but it works anywhere in the world i.e it comes with a roaming plan and costs 10 euros ($13) for 10MB of traffic (20MB for 15 euros). If you want to use the device as a mobile phone then all you need is a suitable SIM with a voice and/or data plan and an loudspeaker and microphone. Of course, the Arduino doesn't run an operating system so don't imagine downloading apps of any sort and the processor is a probably too small to accept a port of, say, Firefox mobile or Android. However, the interface is simple enough — a serial port — to make it possible to consider using it with other devices and the obvious candidate would be the Raspberry Pi which runs Linux quite easily. A Raspberry Pi, Ubuntu Touch or Android plus the GSM Shield would make a reasonable mobile phone.