220-1101 Mobile Devices Practice Question
A user reports that their Android smartphone displays 'Emergency calls only' at the top of the screen and cannot make or receive regular calls. The device still connects to Wi-Fi and can use messaging apps over Wi-Fi. The technician removes the SIM card, inspects it for damage, and reinserts it. The problem persists. The technician then takes a known-working SIM card from another phone and inserts it into the user's phone; the phone immediately connects to the cellular network. Which of the following is the MOST likely cause?
⚠ Common exam trap
It's easy for candidates to confuse 'no cellular service' with a hardware antenna issue or APN misconfiguration, but the SIM swap test is the definitive diagnostic step to isolate a faulty or deactivated SIM card.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SIM card is defective or has been deactivated by the carrier.
The technician's swap test with a known-working SIM card immediately restored cellular connectivity, isolating the issue to the original SIM card. Since the phone could still use Wi-Fi and messaging apps, the radio hardware and software stack for cellular were functional, but the SIM card itself was either physically defective or deactivated by the carrier, preventing network registration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The phone's cellular antenna is disconnected or damaged.
Why it's wrong here
If the cellular antenna were disconnected or damaged, the phone would exhibit poor or nonexistent signal regardless of which SIM is installed. Since replacing the original SIM with a known-good SIM restores full connectivity, the phone's RF hardware, including the antenna and transceiver, must be operational. Furthermore, an antenna failure would likely produce 'No service' or a persistent 'Searching...' state rather than 'Emergency calls only,' because the phone would still be able to detect networks but fail at SIM authentication.
When this WOULD be correct
A user reports no cellular service after a drop, and swapping SIM cards with a known-working phone still shows no service on the original phone but the known-working phone works with the original SIM. This would indicate the phone's antenna or radio hardware is damaged.
- ✓
The SIM card is defective or has been deactivated by the carrier.
Why this is correct
The original SIM card is the root cause because the phone functions normally with a known-good SIM, and the original SIM fails in any other handset. 'Emergency calls only' indicates that the phone can access the network's emergency channel but cannot complete normal authentication for subscriber services. This occurs when the SIM is physically damaged (e.g., fractured chip, corroded contacts) or has been deactivated by the carrier due to suspension, port-out, or account closure.
- ✗
The phone is in airplane mode but Wi-Fi is manually re-enabled.
Why it's wrong here
Airplane mode disables all wireless radios, including the cellular transceiver; if it were active, the status bar would show a specific icon and no signal indicator, not an 'Emergency calls only' message. Even manually re-enabling Wi-Fi while in airplane mode does not turn on the cellular radio, so the phone would remain completely unregistered with the network. The actual condition, where the phone can still reach the emergency channel, proves that the baseband is actively attempting network registration but is being rejected—typically due to a faulty or deactivated SIM.
When this WOULD be correct
A user reports that their smartphone shows 'No service' and cannot make calls or use mobile data, but Wi-Fi works. The technician checks and finds that airplane mode is enabled, and after disabling it, the phone connects to the network. In this scenario, the most likely cause is that the phone was in airplane mode with Wi-Fi manually re-enabled.
- ✗
The mobile network APN settings are incorrectly configured.
Why it's wrong here
Incorrect APN settings only affect packet-data services such as internet, MMS, and sometimes VoLTE provisioning; they do not influence the radio's ability to register with the network. A misconfigured APN would still allow the phone to display full signal bars and place normal voice calls, since voice/SMS traffic uses the control channel and circuit-switched network, not the APN. The 'Emergency calls only' state is caused by a failed registration (typically SIM authentication), so an APN issue is irrelevant here.
When this WOULD be correct
A user can make calls and send texts but cannot access mobile data or send MMS. After verifying data roaming and network mode, the technician checks the APN settings and finds them incorrect. Correcting the APN restores data connectivity.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓The SIM card is defective or has been deactivated by the carrier.Correct answer▾
Why this is correct
The original SIM card is the root cause because the phone functions normally with a known-good SIM, and the original SIM fails in any other handset. 'Emergency calls only' indicates that the phone can access the network's emergency channel but cannot complete normal authentication for subscriber services. This occurs when the SIM is physically damaged (e.g., fractured chip, corroded contacts) or has been deactivated by the carrier due to suspension, port-out, or account closure.
✗The phone's cellular antenna is disconnected or damaged.Wrong answer — click to see why▾
Why this is wrong here
The technician tested a known-working SIM card in the user's phone and it connected immediately, proving the phone's cellular antenna is functional. A damaged antenna would prevent connection with any SIM card.
★ When this WOULD be the correct answer
A user reports no cellular service after a drop, and swapping SIM cards with a known-working phone still shows no service on the original phone but the known-working phone works with the original SIM. This would indicate the phone's antenna or radio hardware is damaged.
Why candidates choose this
Candidates may assume that 'Emergency calls only' indicates a hardware issue like a broken antenna, overlooking the simpler SIM card problem that was confirmed by swapping SIMs.
✗The phone is in airplane mode but Wi-Fi is manually re-enabled.Wrong answer — click to see why▾
Why this is wrong here
Airplane mode disables all cellular radios, but the phone displays 'Emergency calls only' and can still use Wi-Fi. If airplane mode were enabled, Wi-Fi would also be disabled unless manually re-enabled, but the phone would not show 'Emergency calls only'—it would show 'No service' or an airplane icon. The issue here is specifically that the phone cannot register on the cellular network, which is resolved by swapping SIM cards, indicating a SIM problem, not a software mode.
★ When this WOULD be the correct answer
A user reports that their smartphone shows 'No service' and cannot make calls or use mobile data, but Wi-Fi works. The technician checks and finds that airplane mode is enabled, and after disabling it, the phone connects to the network. In this scenario, the most likely cause is that the phone was in airplane mode with Wi-Fi manually re-enabled.
Why candidates choose this
Candidates may confuse 'Emergency calls only' with a state where cellular service is partially disabled, and they know that airplane mode disables cellular radios. They might think that manually re-enabling Wi-Fi while in airplane mode could cause the phone to display 'Emergency calls only' as a transitional state.
✗The mobile network APN settings are incorrectly configured.Wrong answer — click to see why▾
Why this is wrong here
Incorrect APN settings affect data services (MMS, internet) but do not prevent the phone from registering on the cellular network for voice calls. The phone displayed 'Emergency calls only' and could not make regular calls, which indicates a SIM or network registration issue, not an APN problem.
★ When this WOULD be the correct answer
A user can make calls and send texts but cannot access mobile data or send MMS. After verifying data roaming and network mode, the technician checks the APN settings and finds them incorrect. Correcting the APN restores data connectivity.
Why candidates choose this
Candidates may confuse APN configuration as a catch-all for connectivity issues, not realizing that APN settings only affect data services, not voice call registration.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.