MS-900 Describe Microsoft 365 apps and services Practice Question
This MS-900 practice question tests your understanding of describe microsoft 365 apps and services. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses Microsoft 365 Business Premium. They want to deploy a cloud-based phone system for their employees. Which TWO services should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Calling Plan
Microsoft Teams Phone System (formerly Cloud PBX) provides the core PBX functionality—call control, voicemail, and auto attendants—while a Calling Plan (Microsoft's first-party PSTN connectivity) supplies the phone numbers and minutes to make/receive external calls. Together they form a complete cloud phone system without any on-premises infrastructure.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Teams Audio Conferencing
Why it's wrong here
Incorrect. Audio Conferencing is for dial-in to meetings, not a phone system.
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Direct Routing
Why it's wrong here
Incorrect. Direct Routing is an alternative, but not a required service; the question asks for two core components.
✓
Calling Plan
Why this is correct
Correct. Calling Plans provide PSTN minutes and phone numbers.
Related concept
Read the scenario before looking for a memorised answer.
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Microsoft Bookings
Why it's wrong here
Incorrect. Bookings is for appointment scheduling.
✓
Microsoft Teams Phone System
Why this is correct
Correct. Phone System provides the core PBX features.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse Teams Audio Conferencing (meeting dial-in) with the phone system, or think Direct Routing is a cloud-only option when it actually requires on-premises hardware.
Detailed technical explanation
How to think about this question
Under the hood, Teams Phone System uses SIP signaling and Media Bypass to route calls, while Calling Plan leverages Microsoft's own carrier network with direct peering to PSTN providers. A common real-world scenario is a company with no on-premises PBX choosing Calling Plan for simplicity, but if they need to keep an existing carrier contract, they would use Direct Routing instead—though that adds complexity. The key distinction is that Phone System is the software PBX, and Calling Plan is the PSTN trunk.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this MS-900 question in full detail.
Describe Microsoft 365 apps and services — This question tests Describe Microsoft 365 apps and services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Calling Plan — Microsoft Teams Phone System (formerly Cloud PBX) provides the core PBX functionality—call control, voicemail, and auto attendants—while a Calling Plan (Microsoft's first-party PSTN connectivity) supplies the phone numbers and minutes to make/receive external calls. Together they form a complete cloud phone system without any on-premises infrastructure.
What should I do if I get this MS-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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