Quoting Wikipedia, "Advertising is a form of communication intended to persuade an audience (viewers, readers or listeners) to take some action." Other websites, dictionaries etc, cite the similar definition. Advertising executives may have more creative definitions, but they all will circle around the above. Going back to the space issue, my bum is a space, and so is my mobile phone. I understand that. I also understand that I own both of them. One was a birth right, the other I paid for. But, nonetheless, they are BOTH mine.
Now if TATA Nano were to place a sticker on my bum as advertisement, I would politely say no. Ofcourse, if I were a retard, I would charge them a rent. Its still a legal and a better deal than giving free advertisement space. The same policy works for all space owners (billboards, rooftops, office windows, shop windows, toilet seats...). A rent must be paid. But I have control over my bum and can say no. But what about my mobile phone? I own it, I paid for it, I keep it safe, and I take care of it. It is space, but it is mine. So when Grameenphone sends me a barrel of text messages (even at 5am) on my mobile phone, encouraging me to download wallpaper, ringtones, porn, lottery tickets, espn sports updates, real estate updates, and in summary, avail products of other companies, I consider them as advertising on my space.
If they are using my space to advertise, Where's My Rent??