Back around 2000, shortly after The Matrix came out and everyone was buying "those" Nokia phones, I was tasked with writing a couple of applets for a certain UK mobile phone operator.<p>One applet was to design operator logos. The other was to compose ringtones. Both popular things at the time. I was given access to an SMS gateway, a PDF of the Nokia message format and a deadline.<p>The exact UI was phone-dependent, but typically these updates would pop up a confirm box saying "Accept new ringtone?" or something similar. I was surprised to discover that this was triggered by sending an SMS, because there was usually no indication that a message had been received. If you were lucky you would be told where the file had come from, but often the phone just assumed it was an update from the network. On some phones there wasn't even an alert, it would just obey, silently.<p>The message just had to start with "//SCKL", followed by a code, followed by some data. That's it. On first reading I assumed the "header" part would require direct access to the SMS gateway, like the SMTP HELO or similar.<p>Nope. First thing I tried once I had some PoC data was to send a message from my phone directly to a colleague. It worked.<p>Over the course of that project I sent so many of those text messages I still can't get the code //SCKL1581 out of my head. JFTR, sending someone a really awful ringtone (a single diminished fifth or something) is way more annoying than sending them "0" as an operator logo, especially if their phone only has one ringtone.<p><a href="https://www.activexperts.com/sms-component/sms/sckl/" rel="nofollow">https://www.activexperts.com/sms-component/sms/sckl/</a>