Quick Answer
If every smartphone suddenly became unusable while networks and other computers continued operating, the internet would remain online but access patterns would change dramatically. Two-factor authentication, mobile banking, navigation, messaging and app-based services would be disrupted. People with computers, landlines, dedicated GPS units or physical credentials would retain alternatives, so the impact would depend on how much each service assumes a smartphone is present.
Smartphones combine many tools that used to exist separately: phone, camera, map, alarm clock, ticket wallet, banking terminal, authentication device and computer. Losing all of them simultaneously would therefore create a wide range of small failures rather than one single technological collapse.
Communication
Mobile phone networks could continue serving other devices, but billions of people would lose their usual personal endpoints. Messaging apps would still run on computers and tablets where available. Landlines and workplace systems could provide alternatives, but the convenience of always-carry communication would vanish.
Navigation
People would fall back on dedicated navigation devices, printed maps, vehicle systems and local knowledge. The most noticeable change would be for pedestrians and travelers who currently depend on a phone for turn-by-turn directions.
Authentication and banking
Many services use phones for one-time codes, authentication apps or push approvals. Banks and websites would need alternative verification channels. Services that had already planned for lost or stolen phones would be better positioned than systems designed around one device being permanently available.
Work and logistics
Delivery drivers, field workers and businesses that use mobile apps for scheduling or proof of delivery would experience immediate disruption. Some operations could switch to laptops, radios or paper processes, but the transition would be slower and more labor-intensive.
Established scienceA smartphone outage is not the same as an internet outage. Servers, fiber networks, data centers and other computers can continue working even if a major category of client device disappears.
The bottom line
The smartphone has become an access layer between people and many digital systems. Remove it and the underlying internet can remain alive, but everyday access to navigation, identity, communication and services becomes much more cumbersome.
The immediate loss would be personal communication and mobile access, but the larger disruption would come from systems that quietly depend on smartphones as interfaces: authentication, two-factor codes, navigation, payment terminals and field-work tools. Some services would continue because their underlying networks and servers still exist. The scenario is therefore less about the internet vanishing and more about a major human interface layer disappearing.
The second-order effects