The original phrase was: "the revolution will not be televised" and it was a poem and song by Gil Scott-Heron. It was the B-side to Scott-Heron's first single, "Home Is Where the Hatred Is" (1969 or 70). The poem can be found here:
The bitter irony is that the original poem expressed the sentiment that complacency, television culture and capitalism were not the route of change and that the truth cannot and will not be accurately mediated by by those in control of the images that you are fed (the media and the international conglomerates) but rather that it, the revolution and the truth exist out there, that they are live.
Yet when rappers, songwriters and commercials use the phrase these days, they more commonly state: "the revolution WILL BE televised" meaning that the song, rap or product you are viewing IS the revolution. In other words the rapper/songwriter is supposedly bringing the revolution to you in the form of his/her lyrical stylings-- lame, considering.
Hope this helps.