If you've mastered the art of Arduino, but haven't yet been brave enough to toss in a bit of GSM communication, the how-to guides linked below definitely deserve your attention.

This will allow the development platform to connect to the internet via GSM mobile phone networks. The module, or shield, was developed in conjunction with Telefónica’s Physical Internet Laboratory ...

Now that tinkering has finally come to fruition with [Phang]’s TraLog shield, a single Arduino shield that combines GPS tracking with a GSM and GPRS transceiver.

Arduino devices have had the option of a GSM linkup for awhile, but getting that cellular link to truly strut its stuff hasn't always been easy, even for those of us who'd be inclined to program ...

The GSM Shield also includes a Telefonica SIM card that includes a worldwide data tariff which can be used anywhere there is a cellular signal. Features include the ability to have the Arduino ...