The years covered here, 1800-1855, represent a period when stampless letters grew, peaked and waned. Around 1800, paper began to be circulated on a more popular venue, as it was produced en-mass by industrialized methods. Starting here we see an increase of letters, or what more formal institutions call "papers" or "personal documents," or just plain "documents," and of course philatelists call them "stampless letters." Is there a problem with semantics? A lot of people in these fields do not think so, but I do. In order to create an increase in accessibility, keywords must be adopted.
I have just seen that the 4th Annual Postal History Symposium, hosted by the National Postal Museum of the Smithsonian Institution in 2009, (held at the APS headquarters in Bellefonte, PA) has at least two papers that are relevant to the stampless letter: First is Catherine J. Golden's
“Why is a Raven like a Writing Desk?” - Post Office Reform, Collectible Commodities and Victorian Culture [paper | presentation]
and second, Michael Laurence's Icons of Reform, Postal and Otherwise
[paper | presentation]
As far as I know, Golden is not a philatelist, but an academic looking in at the subject. Laurence is a well known philatelist looking outwards. However, I have yet to read these articles in depth.
Whatever this stuff is called, the general public started to utilize it as a medium for communication, and with increasing production, left more of it lying around for today's historian to analyze. Volume peaked in the 1840s. But in 1844, Morse Code entered the world. This was possibly the biggest invention for communication, and one that truly started an era known as the Information Age, in my opinion.
It appears from what is seen at auction, in holdings, accumulations, and collections, the years 1845-51 produced the greatest amount of stampless letters being written. This is only an educated guess. In 1855, the United States Post Office (USPO) made stamps compulsory on letters beginning Apr. 1, 1855. Scholars, and I can not say I am one, know more about the competition in communication after 1855, which might be looked at as between the USPO, the telegraph, and to an extent rail and ships, as these two became faster. But what about newspapers? Possibly they were the only medium to battle stampless letters for information.
Even with papers, the USPO dominated communication from its inception in 1789 until the telegraph gained more widespread use in the 1850s. Post offices were built around the country to take in and deliver mail, i.e. communication. In fact, it is possible to gauge the amount of mail sent by looking at USPO records. However, even though the post office grew after the introduction of the telegraph, it did not grow as fast. It lost its monopoly as a vehicle for communication.
Stampless was rendered old. It was, in fact, old when it became popular. Huh? Yes, as its use increased by virtue of a better travel network, that network was exploited by the USPO w/ the introduction of stamps in 1847.
Scott #1 - 1847 Mint 5c Franklin, Value $6750.00 (2012)
Not popular at first, stamps became dynamic for the public because one did not have to go to a post office to mail a letter. Of course, not everywhere could this be done. It really only was possible in the area between Washington DC and Boston. Stamps were the now, the wow, the more efficient way for Americans to send their letters. For the USPO, stamps were the vehicle to stay profitable against new forms of technology. In 1851, the USPO gave an incentive for the public to use stamps. A 3c stamp was offered to send a letter up to 3000 miles, but if not prepaid, it was 5c. This was only the latest indication of rates going down through the efficiency of physical travel. Incredibly, the rate would fall even further to 2c in any territory or state in the geographical area of what would eventually become 48 states. The rate would not rise to 4c until 1958; a span of 107 years!