Twitter is expanding its relationship with American Express to allow Amex cardholders to tweet to purchase goods online and have them delivered.

In March 2012, American Express launched Card Sync, a service that enables cardholders to obtain discounts in merchants' stores by tweeting special offer hashtags. The service now provides a mechanism to tweet hashtags as a means of purchasing American Express Gift Cards and products from partners Amazon, Sony, Urban Zen and Microsoft Xbox 360.

To use Card Sync, Twitter members with Amex cards must visit the American Express website and grant permission for Card Sync to access their Twitter account. Those who previously enabled Card Sync with Twitter for couponless offers will have to revisit the American Express website to enter shipping information.

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To those participating in Card Sync, American Express is offering the equivalent of free money: Until Sunday, March 3, the company is selling a $25 Amex Gift Card for $15 to participating cardholders who tweet #BuyAmexGiftCard25 (one per customer).

Starting February 13, at noon EST, American Express plans to release a list of discounted product hashtags through its Twitter feed. The list includes products like the Amazon Kindle Fire HD for $150 (regularly $199) and the Sony Action Cam plus a waterproof headband mount for $180 (regularly $180 for the Action Cam and $30 for the headband mount). American Express says shipping will be free.

The advantage of this particular program for American Express is that the company earns something back for the discounts it's offering: The advertising value of customer tweets. In a statement, Leslie Berland, senior VP of digital partnerships and development at American Express, calls the arrangement a "closed-loop network to introduce a seamless solution that redefines what's possible in the world of social commerce."

For Twitter, the arrangement brings microblogging and e-commerce closer together, thereby improving the company's position for the stock offering it's expected to make later this year or next year.

Twitter appears to have laid the foundation to transform itself into a profitable public company. In September 2012, research firm eMarketer estimated that Twitter earned twice as much on mobile ad revenue ($116.8 million) as Facebook did during the same period ($72.7 million). And a New York Times report suggested Twitter will generate $1 billion in revenue overall in 2013.