They also only implement serial sending (so the Arduino receives) so far, although they mention the next step would be to build the other side of the connection.

That is because the Arduino is just sending tiny movements, each of which is a code that represents a nybble (4 binary bits) of data.

Particle’s Electron is a “cellular Arduino” with a global data plan ARM- and GSM-based board promises quick on-ramp for mobile IoT development.

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 ...