They give away one iPhone per day and the contest runs till July 7, 2009. Continue reading for details on how to enter the contest.
The contest is open to anyone around the world. All you have to do is to tweet about anything (on Twitter of course) with the #squarespace hash tag -which is already the most trending topic on Twitter.
You can tweet as much as you like, gaining you more than one entry in the contest. The winner of the contest would be chosen by a random draw each day, and would be contacted by SquareSpace. To keep things fair, if you happen to win, you wont be able to participate in the subsequent draws.
Even though the contest is open to everyone around the world, you may still not be able to get the 16GB iPhone 3GS if its not officially available in your country. Though you can still redeem the $199 gift certificate towards any other Apple product, or if you are creative enough, find a way to get that iPhone 3GS (probably via a friend/relative in another country).
You can get more details on the contest along with the official rules and regulations here.