I would assume much longer. I have a recollection [i.e. I cannot build a google query to find a reference right now] of some poor schmuck working with a tribute band who asked him to send a text message of the lyrics to "Machine Gun" (a Jimi Hendrixs song). Something along the lines of 'please send us machine gun'. He promptly replied with the words and a few hours later was on the wrong end of an armed response team storming his house asking where the machine gun was.

At the time the only explanation he could think of was his messages were being intercepted but this was denied and the official explanation was he had supposedly sent the reply text to the wrong person who called the police. His phone logs showed he sent the reply text to the correct number but the police just dismissed this with no explanation.

Now we have a more plausable explanation. This has apparently been going on for a long time.

[Edit, for clarity, this was in the UK.]