It began with an early, hopeful promise — that one day, very soon, you could commonly start paying for goods and services with a tap of your phone. Not with an app on your phone, mind you, but with a reader at the cash register that would instantly and wirelessly complete your transaction.

That future, sadly, hasn't yet materialized. In fact, if anything, we seem to be retreating from it.

The first sign came last year, when PayPal debuted a physical debit card in a partnership with Discover. The card grants its users access to all of their PayPal-linked accounts and, according to a company spokesperson, can now be used in hundreds of thousands of locations nationwide.

More recently, a little startup known as Coin has caused a ruckus by promoting a similar idea: An all-in-one credit card that not only consolidates your payment cards — and lets you selectively choose among them with a single tap — but also sends your phone a notification when you've left it behind someplace. Coin began last week with a modest crowd-funding goal of $50,000. Within 47 minutes, the project had taken 1,000 preorders.

Now, the company with the world's biggest smartphone platform is following suit. Google has unveiled a debit card for its Wallet app, and while the thing itself is pretty much what you'd expect, the move is surprising. Google was one of the earliest proponents of NFC, or the technology underpinning the tap-to-transact dream.

Even when NFC failed to take off, other alternatives sprung up. Square Wallet is a pretty elegant way of handling mobile payments (you just give your name at the register and go). Yet apparently enough people still prefer paying by card that Google thinks it's a worthwhile audience to go after.

PayPal implicitly recognizes this, too.

"Our strategy is to be everywhere our consumers are," company spokesperson Kathy Chui told me. "We also want to work with merchants. So there's going to be some situations where it's going to make more sense to have a card and there are going to be situations where people want to use mobile payments in stores."

The persistence of plastic suggests we're a lot farther than we think from a world where true mobile payments are the norm.

One notable counterexample lies in Bitcoin, the online currency that effectively turns every transaction into a mobile payment. Because many vendors, even real-world ones, complete the transaction by showing you a QR code that you scan with your phone, no physical tender is ever exchanged. But it's still a nascent currency, subject to all the risk that implies. Only a tiny fraction of the brick-and-mortar retail locations in your city will accept Bitcoin payments.

Paying for goods and services with your smartphone might become de rigueur eventually. But for now at least, we're taking a little detour.