The signal wasn't noticed immediately. It had been relayed for years, but was lost amongst the frequencies that had been deregulated for mobile phone usage. As everyone knows, nothing of particular consequence happens on a mobile phone call, so no one was listening.
Dan Wills was the first human to notice the pattern. Dan, for the past year and a half, had been An Alltel "signals engineer," a title which always made him feel a bit uncomfortable. He was on his lunch break, fooling around with his new signal detector. The detector measured faults causing errors in wireless transmissions by attempting to locate anomalies in radio frequency communications between equipment parked in mobile phone towers in the area. This was a hell of a lot better than actually climbing each tower to analyze equipment failure, which his previous job at Alltel used to require. He disliked that intensely: "I'm going to climb the tower if I have to... wait.... er, nevermind."
For years, the mobile-phone-owning populace of Deride, the town which he was currently pointing his detector in, had been complaining of poor mobile phone service. It was not an unprofitable market, and the usual companies had tried the usual remedies. They'd installed new towers, they'd cranked up the signal strength of the equipment in each tower, they'd installed even more smiling, developmentally disabled customer service representatives. But nothing had worked. If you lived in Deride, you had the shortest possible mobile phone conversations, because you literally never knew how long you'd have to talk. "Milk, break, over." "Roger, arrive 18:00 hours, over."
Unless you're self-employed, any conspicuous demonstration of competence while performing your job is a sign of ignorance. Of this, Dan was keenly aware, and he thus sandbagged his way through his workday, preferring to dedicate any intelligence he possessed to interests outside the workplace. As a result, the company for which Dan worked believed he was just barely self-aware meat. But he refused to not show up, and so they had given him the simplest possible job at the lowest possible pay scale.
Dan was keenly interested in communications technology. His new device afforded him some interesting new diversions. For instance, being something of a conspiracy buff, he had lately become on the lookout for anomalous radio frequency patterns. It was possible to use the mobile phone frequencies for simpler digital communications, hiding communications "in plain sight" via a form of wireless steganography. Dan continually suspected that a local Al Quaeda terrorist cell was using this mode of communications to send and receive what he imagined were vitriol-laden fatwahs. Although Dan didn't actually know what a fatwah was, and although his was an absurd assumption (as it's far cheaper and easier to use standard communication channels with encrypted data), and although no self-respecting terrorist cell would have parked themselves in Deride, Dan had fun attempting to make sense of the anomalies he detected in communications by affording himself this delusion.
While he couldn't have possibly cared less about the mobile phone health of the good citizens of Deride (he didn't really like the telephone much anyway), he did become interested in one particular RF anomaly that appeared to happen once every six minutes. Six minutes was curiously the longest mobile phone conversation anyone in Deride had ever had, but Dan didn't know that.
Precisely every six minutes, a transmission would squelch all other communications on a wide band of the mobile freqency. Each transmission was in the form of a short burst of nonrandom information, which, to Dan, seemed like very crude Morse code. But it wasn't standard, literal, Morse code. Literal morse code elides some of the most frequently used letters: a single "dit" is an "E", for example. The strange signal was not like this, it used different patterns.
The other strange thing Dan noticed was that the signal's origin was from somewhere beyond communications satellite orbit. Dan could tell this because of the "angle" of the communications received by the analyzer. He had previously seen and analyzed stray transmissions from satellites on the frequencies reserved for mobile phone usage, or something. At least let's pretend he did for the purpose of the furthering of this story, because frankly I can't think of a scientifically reasonable way Dan would be able to tell the origin of the signal, so let's all suspend disbelief.
This code was different, but, intrigued by its origin, and as an employee for a large company, Dan had little else to do but than to decode it. It took him roughly three days, all of which were filed in his timesheet as "analsyis".
When Dan finally did decode one of the six-minute-spaced messages, which happened to be the first transmission ever received from a nonhuman intelligence, it read:
He needn't have read further, the rest was the same.