For American Express customers, making a purchase is as easy as sending a tweet. The credit card company has upgraded its Twitter Sync program allowing cardholders to pay for products using a hashtag.

Originally launched last March, Twitter Sync enabled customers to get discounts by tweeting offer hashtags. The deal is automatically applied to the card, requiring no printing. Taking it a step further, AmEx has integrated payments.

Now payments can be made by tweeting a purchase hashtag and retweeting the confirmation tweet from AmEx — this must be done within 15 minutes of receiving it. The item purchased will then be shipped to the billing address synced with Twitter through free two-day shipping.

Currently the payment service is limited to participating merchants in the U.S., such as Amazon, Sony, Urban Zen, and Xbox 360. The company said a full list of product hashtags will be available on Wednesday, February 13th at noon EST.

If successful, tweet-to-buy hashtags could soon appear in TV commercials and other advertisements. The downside is that by limiting the functionality to AmEx, only a small portion of consumers will be eligible to participate. However, it’s possible this will open doors for other card carriers.

You can learn more about how AmEx’s Twitter Synch and payment features work in the video below.

[Via: TechCrunch, Image credit: Images Money]