And what if those menus are in some foreign language I don't understand? And how would that work with cash? I'd have to fork over my credit card (assuming that's even an acceptable form of payment) and may end up with a recurring charge for a cell plan in a country I'll visit for a week.

Visions like yours are nice, but my money is what we'll actually get is a far crappier, buggier version.

One impossible-to-replace benefit of physical objects is that you can use physical control to place limits on them. Pay with cash, no recurring changes, move the card, move the service. Theoretically you could do that in software, but practically you won't because those are expensive features that almost always get cut.