Send real postcards to your family and friends with SendIt4.me, now available as an iPhone client. The application is 100% free and each postcard you send will cost $2USD. The postcards can be sent anywhere in the world, and postage time is dependent on your international and local mail services (they are posted from the US, so if you live there you should get it quicker).
Sidenote: I submitted this application initially to Apple on the 18th Jan 2009. It was finally approved tonight. There was only 1 "Please wait" mail, and one "We need some help testing it" mail - too long in my opinion.