"Would you like to put that on your Bloomingdale's card today?"

"No, let me try something high-tech here," I replied. It's the stock statement I make to sales clerks right before I try to pay with Google Wallet so they don't get concerned or confused when I wave my phone instead of pulling out my actual wallet.

As usual, I turned the Galaxy Nexus's screen on and held it flat against the contact pad right above the signature capture device, the one you use when you pay with a normal credit card. The Google Wallet logo appeared, the phone briefly vibrated (usually a good sign). The display on the kiosk changed from "Swipe Card" to "Processing...," and I assumed we were off to the races.

But I waited. And I waited. And I waited. The clerk, obviously a bit annoyed with my antics, held an icy stare on me while we both twiddled our thumbs, waiting for his point-of-sale system to do something.

"Is it doing anything?" I finally asked, more to break the tension than anything else — I knew the answer already. "No, I'm not seeing anything on my screen," he responded, deadpan. I felt his pain. At that point, I just wanted to pay the old-fashioned way and get out of there.

After a few more seconds, a "receipt" came up on my phone's screen, saying that the transaction couldn't be verified and that I should check with the cashier to see if it had gone through. Well, he certainly didn't know anything, so there we were — stuck — debating the likelihood of whether my payment had been processed. From his perspective, it didn't really matter anyway: the cash register hadn't completed the sale or spit out a receipt, so as far as he was concerned, I hadn't bought anything yet.

Eventually, the clerk offered that he could "clear the screen," which would allow me to swipe my card. It didn't really sound like a thoroughly satisfying resolution to the problem, but at least I'd be able to get the stuff I'd come in to buy. So I said "go ahead."

And you know what? It worked. Flawlessly, the first time, with no drama.

Of course it did. That's the way it's been for decades with credit and debit cards: once in a blue moon, you might be told that the retailer's "machines are down," but otherwise, they just work. They're practically as reliable and as ubiquitous as cash. Naturally, the world's credit card infrastructure has had decades to develop and settle, but it feels as though they grew out of the same "99.99999 percent uptime" mentality that our legacy telephone service did — a mentality not shared by the wireless industry that's replacing it (largely for practical reasons of spectrum exhaustion, unpredictable reception, and overwhelming complexity compared to a pair of copper wires).

The inherent unreliability of cellular networks is one matter, but currency simply can't fail. It needs to be — to borrow some verbiage you may be familiar with — legal tender for all debts, public and private. Until that happens, it's nothing more than a novelty because you're unable to rely on it: you need to operate under the assumption that you might not be able to use it to pay, which leaves you no option but to carry cash (or a credit card) anyway. There's nothing worse than being stuck without any way to settle a bill.

So while I love the concept of Google Wallet, ISIS, and services like them, they share a fatal flaw: I can't trust them, because there's too much technology involved — and a surplus of technology inevitably leads to unreliability. I can show them off to friends, dazzle unsuspecting clerks, and use them to do weird things at self-checkout kiosks, but mobile payments can't be a cash equivalent now or any time soon. They're a gimmick. You approach the counter thinking "what the heck, let's give this a shot."

Oh, and in case you're wondering: I bought some fancy mixing bowls.