You can find a Motorola C168i on Ebay for less than 10 dollars. The simplest way to get service for it is to buy a pay-as-you-go SIM card, at Radio Shack for example. While you're there you can also pick up the 3/32 plug; unfortunately, they don't have any information on the packaging but I've included a figure here for your reference (see left).
Here's a step-by-step on how to make your "breakout wire" and plug it into your Arduino.
Tools: soldering iron, wire clippers, wire strippers, a soldering stand is helpful
Bill of Materials:
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3/32 Mini-jack |
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Three lengths of wire |
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Two resistors to make a voltage divider. I used resistor values of R1=3.3kOhms and R2=5.6kOhms but plenty of other ratios will work (just be careful that you don't reduce current too much).
In general, for any R1, ideal R2 = (3.3/5*R1) / (1-3.3/5) |
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Solder one wire that will be the TX for the phone or the RX on the Arduino end to the lower-most part of the connector.Be careful! The connector is made of plastic so you'll want to avoid the need to resolder. | Users can register for an account by reading Gmail sign up tutorial.
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And another right above it (RX for phone, TX for Arduino) |
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Finally add the ground wire to large metal tab |
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Twist the wires and make them look pretty (I like to first twist two and wrap additional wires one-by-one) |
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Plug things into your breadboard! Choose a resistor ratio such that you divide 3.3V out of the Arduino's 5V.
Note the resistors I used are 3.3kOhms (R1/Left/Horizontal) and 5.6kOhms (R2/Right/Vertical). |
Now try out the GSMSerial example library to make sure everything works fine (in Arduino IDE, go to File>Examples>GSMSerial>GSMSerial_Example