It is still early days for each of these companies, and as the Pew survey suggests, it is difficult to say whether they will gain widespread acceptance or freak people out — or whether, indeed, they will improve our well-being. With so much vital data in our cellphones, what happens when we lose them? Could we one day load up the cellphones of our teenage children with money for cab rides but not beer? Would cash be reserved for purchases of sex, drugs and, in repressive countries, banned books? Or just for people with bad digital reputations?…

“The physical wallet, which had no innovation in the last 50 years, will become an artifact,” John J. Donahoe, the chief executive of eBay, told me recently. The wallet would move into the cloud, and ideally, from his perspective, into PayPal. No more would the consumer worry about losing a wallet, nor about organizing coupons and loyalty cards. Everything, he declared, would be contained within PayPal. It would also enable the company to collect vast amounts of data about customer habits, purchases and budgets…

I recently described PayPal’s plans to Alessandro Acquisti, an economist who studies digital privacy at Carnegie Mellon University. Mr. Acquisti smiled. If today all you need to do is enter your phone number and PIN when you visit a store, perhaps tomorrow, he said, that store will be able to detect your phone by its unique identifier as soon as you enter. Perhaps in the not-too-distant future, he went on, you won’t have to shop at all. Your vast piles of shopping data would be instead collected, analyzed and used to tell you exactly what you need: a new motorcycle from Ducati, perhaps, or purple rain boots in the next size for your growing child. Money will be seamlessly taken from your account. A delivery will arrive at your doorstep. “In the future, maybe you won’t have to pay,” Mr. Acquisti offered, only half in jest. “The transaction will be made for you.”