I recall seeing this in movies. Can it be called the poor man's steel?
Absolutely not. A honing steel is significantly harder than the blade of a knife and is specially textured for honing.
Rubbing two knives together is more likely to dull or knick the blades than anything else.
The blade of a knife should never touch anything harder than a wooden cutting board. Not glass, not granite, and certainly not steel (except for honing/sharpening).
I wouldn't recommend it -- it can be done, but I think it's more for show than anything else. They're actually pulling the edge of one knife against the back of the other one.
My mom used to always use the bottom of a plate to hone (sharpen) ? her knives. The plates were glazed stoneware, but the bottom was unglazed. We never had a steel that I can remember.
Most home chefs aren't putting their knives through as much work as professional chefs, and likely aren't as aggressive with their knives, so likely don't need to be as worried about honing, so long as they're following @hobodave's advice (no glass cutting boards!), take care of them (no dropping them in the metal sink with glasses) and aren't hacking through bones.
you can only hone a knife against something harder than itself. steel on steel isn't such a good idea, the edges are so thin that you'll damage the edge.
ceramic (like plates), glass, and stone are all harder than your blade, but difficult to use as a sharpening tool (although it can be done)
i'll validate that home cooks don't punish their knives through proper use as much as professional chefs do, but they still will need to sharpen their blades eventually. honing will keep the blade "sharp" in the interim and restore a dull blade to a sharp state. it's when you hone a blade and it's no longer sharp than you have to get the blade re-sharpened properly - not an easy task. (and another topic)
purchase a steel and learn to use it. it's one of the most valuable skills in the kitchen (and underused). it doesn't even have to be expensive, even a $20 steel can do wonders to a $150 knife.
NOTE: even a factory edge can be made to be sharper through careful sharpening / honing techniques.
Years after the question was asked, but actually you can sharpen a knife on the back of another knife. I was even taught to do this by a chef when working as a cook. But, you are not grinding a sharp edge on the knife, you are burnishing a slight burr. This is a lot more like the way you put an edge on a cabinet scraper, though with the burr aligned with the blade rather than at a right-angle. https://en.wikipedia.org/wiki/Card_scraper (I am fairly sure that a sharpening steel works this way too, they don't have an actual cutting-tool geometry)
It can definitely be done if you are used to it, especially if you sharpened your knife and know the angle. I always hone my knives on other knives. I have a solid steel chef's knife (by that i mean no plastic/wooden handle) which is really hard, 0 elasticity, and I regularly hone the rest of the knives on it (usually smaller). By doing that I actually keep that knife razor-sharp as well as all the others.