(FILES) A picture taken on October 23, 2012 shows the screen of a blackberry phone featuring a page with the adress of the US micro-blogging Twitter website. (FRED TANNEAU/AFP/GETTY IMAGES)

Twitter and American Express have joined up to “unlock the purchasing power of the #hashtag” by allowing eligible cardholders to buy things by appending a special tag to the end of their Twitter messages.

The deal was announced Tuesday evening, and users can already buy a $25 American Express gift card for $15 by tweeting a message with the tag: #ButAmexGiftCard25. American Express said that it will release more Twitter buys at noon Feb. 13.

These include offers for the Amazon Kindle Fire HD for $149.99, a Sony headband camera for $179.99, an Xbox console for $179.99 and a bracelet from Donna Karan for $80. Customers will also have to pay taxes on the items. These offers will expire March 3, or as supplies last.

The two companies have partnered since March to offer discounts and deals, but this is the first time that users will be able to have goods shipped to them.

The process works like this: Users who have joined their American Express and Twitter accounts will add a certain product hashtag to their tweets and then receive a reply from the American Express @AmexSync account containing a confirmation hashtag. Users then have 15 minutes to tweet that confirmation hashtag to confirm their purchase. Products will then be shipped to users’ billing addresses. American Express says it will provide free, two-day shipping.

The deal allows Twitter to try out the mobile e-commerce market — the company recently said that 60 percent of its 200 million active users log in through a mobile device at least once a month.

Those using Twitter primarily through their mobile devices are some of the service’s most engaged and active users, the company said. They tend to be younger and are a whopping 169 percent more likely to use Twitter while shopping than the average tweeter. They are 86 percent more likely to be on Twitter many times during the day and also tend to eschew the network’s desktop site, which advertisers would be smart to note as they evaluate how to split their ad investments between desktop display ads and mobile marketing campaigns.

E-commerce, and mobile commerce specifically, are growing trends in the retail world. E-commerce spending topped $1 trillion worldwide for the first time in 2012, according to data from eMarketer, and sales are expected to grow as much as 18.3 percent in 2013.

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