Off the bat I found http://www.payphone-project.com/mailboxes/ and http://www.mailboxmap.com/ - probably coulda guessed that second one, which appears, at a glance, to be a little bit easier/quicker to use.
Good lookin out dude. I saw the first one too but it was super unreliable and not user friendly. that second one is the beez neez. thanks!
Okay the seal on the back of this letter looks suspiciously like the last letter - is that your signature seal or something?
Mua ha ha ha!