If the phone works on Wi-Fi but not off Wi-Fi, the most likely issue is that cellular data is disabled (or restricted). This aligns directly with the CompTIA A+ objective language for mobile troubleshooting, which explicitly includes “wireless/cellular data network (enable/disable).” After travel, users often enable airplane mode or disable cellular data to avoid roaming charges, and sometimes forget to re-enable it.

Quentin Docter’s mobile connectivity discussion repeatedly distinguishes Wi-Fi access from cellular connectivity and treats cellular settings as a primary area to verify when Internet access is not available away from Wi-Fi. While data caps/limits could throttle service, they usually don’t make all non-Wi-Fi browsing and email impossible immediately. VPN issues might block some access, but the simplest “most likely” resolution based on the symptom is re-enabling cellular data. Reinstalling the SIM is possible, but again not the first, most likely fix given the scenario framing. Therefore, Enable cellular data (A) is correct.