http://www.touchnote.com/mobile
You can take a picture with your phone, e.g. take a picture of a vacant house, and the picture will be on one side of a postcard. You can put your message on the other side, e.g. "I really want to buy this house!", and send it to whomever you want, e.g. the owner of the house.
It's about 2 bucks per card.
Or you could take a picture of you, your kids, ice cream, kittens, or whatever, and send it to your mom, friends, relatives, boss, or whomever, and they will probably keep it on the refrigerator, mantle, bookshelf, or something.
