From the site- "The World's Smallest Postal Service is a teeny tiny letter transcription service - now available online. Here's how it works: You write a letter (up to 120 words! - see the form below) and I transcribe it onto tiny stationary (1 x 1.5 inches) with a magical transcription device. It then goes into a tiny envelope which gets addressed, stamped, and sealed with a miniscule wax seal with your initial on it. The letter then goes into a see-through folded coin case and is packaged up with a magnifying glass in a larger glassine envelope, finished off with a large "World's Smallest Letter" wax seal. It is then put in a sturdy mailer for shipping. I can send your letter directly to a recipient of your choice, or to you if you would like to distribute it yourself."
For more information and prices go to Leafcutter Designs.