A new partnership between PayPal and Discover is another step towards merging online and offline payments. PayPal has announced that in 2013, Discover will work with it to let merchants who take Discover cards accept PayPal as well. According to AllThingsD, buyers will be able to use PayPal charge cards or enter their phone number and PIN starting next April. The companies promise that merchants won't have to buy new hardware or upgrade software. In time, PayPal could also offer things like check-ins or loyalty programs.

PayPal is already testing mobile payments at McDonald's restaurants in France, and it has its own partnerships with US retailers, but the company says this deal will bring its payments to 7 million locations across the US, with the possibility of international expansion. That's orders of magnitude larger than a recent deal between Square and Starbucks, which will allow Square mobile payments at the coffee shops.