Dronecell

Dronecell is, in essence, a cellphone with input and output points to allow interaction with a micro controller.
You can output data, voice, sms and even pwm. This would allow you to control your arduino from anywhere in the world with a phone or computer as long as the dronecell is in range of a phone mast.

Only one problem:
They seem to have disappeared from sale.

Anyone know why?

This device could be a direct threat to the manufacturers of radio control and FPV equipment as one of these devices @ around $100 could blow away the need for their gear and offer unlimited range capability instead of a few miles.

There are a number of Arduino-compatible GSM modules for sale, and they do all those things.