We have free instant payments in the Eurozone, UK has had them for about a decade and I'd say PayPal is doing fine (unfortunately). So what's the concern?
I used to work on for a company on a product that did exactly this, but the company stopped working on that product since it didn't go anywhere (API docs seem to still be online though :D https://docs.satoshipay.io/api/).
Some small publishers liked it, big ones wanted to force their customers to subscribe (whilst recording their data at the same time).
I really like the general idea though and hope it does make a comeback. I think it would be good for review/test sites especially.
This can be enabled or disabled under the System Settings > Battery > Options > Wake for network access (Always / Power adapter / Never). Or possibly the phone registers it as connected for a while after it sends its last packet?