220-1101 Mobile Devices Practice Question
A user reports that their Android smartphone can make and receive phone calls, but cannot send or receive text messages (SMS/MMS) after a recent operating system update. The user has verified that the mobile data connection is working, and the messaging app is not blocked. Which of the following is the MOST likely cause of this issue?
⚠ Common exam trap
CompTIA often tests the distinction between services that rely on the cellular voice/data path versus those that depend on specific configuration parameters like the SMSC, leading candidates to mistakenly blame the SIM card or app when the issue is a misconfigured carrier-specific setting.
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 SMS center number settings are incorrect.
The SMS center number (SMSC) is a critical parameter stored on the SIM card that routes outgoing text messages through the carrier's SMSC server. After an OS update, this setting can be reset or corrupted, preventing SMS/MMS transmission while voice calls and mobile data remain functional because those services use separate network paths. Correcting the SMSC number restores SMS functionality without affecting other services.
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 SIM card is not properly inserted.
Why it's wrong here
A SIM card that is not properly inserted would prevent the device from acquiring the carrier network entirely, making voice calls and SMS impossible. Since the phone successfully places and receives calls, the SIM is clearly seated, recognized, and authenticated by the network. Therefore, a loose or missing SIM cannot be the reason only text messaging fails.
- ✓
The SMS center number settings are incorrect.
Why this is correct
The SMS Center (SMSC) number is a carrier-specific address that tells the phone where to route outgoing messages; if it's incorrect or blank, the network rejects the SMS transaction while voice calls remain unaffected. Some Android OS updates are known to overwrite or reset the SMSC to a default value that doesn't match the operator's gateway. This causes instant 'Send failed' errors, even though the phone has full signal and call capability.
- ✗
The phone is not connected to a Wi-Fi network.
Why it's wrong here
SMS and MMS are delivered over the cellular radio network—either via legacy circuit-switched signaling or via IMS on modern LTE/5G—not over Wi-Fi. A device with no Wi-Fi connection will still send and receive texts normally as long as it has a registered cellular network. Thus, being off Wi-Fi has zero bearing on the reported SMS failure.
- ✗
The messaging app is corrupted.
Why it's wrong here
A corrupted messaging app would typically produce continuous crashes, a black screen, or an inability to open the app, and the user has already verified that the app is not blocked or disabled. Moreover, the SMS failure is consistent across the system (including the stock app), pointing to a network-level setting rather than an application-local glitch. Clearing the app's cache might not fix an invalid SMSC, so this is a secondary suspect.
Go deeper
Related to this question
Learn chapter
Mobile Operating Systems: iOS and Android
Key term
Operating system
An operating system (OS) is the core software that manages a computer's hardware and software resources, providing common services for computer programs.
Key term
SIM
A SIM (Subscriber Identity Module) is a smart card that securely stores the international mobile subscriber identity (IMSI) and related key used to identify and authenticate a subscriber on mobile networks.
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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.