Business Phone Systems Cheat Sheet 2026

The 30 highest-yield Business Phone Systems facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What is least-cost routing (LCR) in a PBX? → Automatically routes outbound calls over the cheapest available carrier or trunk
2. What is codec negotiation in SIP call setup? → The process where two SIP endpoints agree on which audio codec to use for the call
3. What is call screening? → Announcing the caller's name or number to the recipient before they accept the call
4. What does NAT traversal solve in VoIP deployments? → Allows VoIP traffic to pass through network address translation firewalls
5. What is a toll-free number prefix used in the United States? → 800 (and 888, 877, 866, 855, 844, 833)
6. What does 'number portability' allow a business to do when switching cloud phone providers? → Keep existing phone numbers when moving to a new service provider
7. What does PBX stand for? → Private Branch Exchange
8. What does 'follow-me' call routing do? → Rings a sequence of phone numbers until the call is answered or goes to voicemail
9. What does 'echo' in a VoIP call typically indicate? → Acoustic echo from a speakerphone or sidetone misconfiguration in the phone hardware
10. Which FCC regulation requires businesses to maintain internal Do Not Call lists and honor consumer opt-out requests? → TCPA
11. What is a VLAN (Virtual Local Area Network) used for with VoIP phones? → Separates voice traffic from data traffic on the same physical network for better QoS
12. What does a '503 Service Unavailable' SIP error response indicate? → The SIP server is overloaded or temporarily unavailable
13. Which protocol is most commonly used for signaling in VoIP systems? → SIP
14. Which port does SIP typically use for unencrypted signaling? → 5060
15. What security measure helps prevent unauthorized SIP registration on a business phone system? → Using strong, unique SIP passwords and restricting registration to known IP address ranges
16. Which type of denial-of-service attack specifically targets VoIP infrastructure? → SIP INVITE flood attack
17. Which transport protocol do most VoIP systems prefer for carrying RTP media? → UDP
18. Which protocol is used to encrypt SIP signaling messages and protect VoIP call setup from interception? → TLS
19. What information is typically required to provision a new IP phone on a cloud system? → MAC address of the phone, assigned extension number, and SIP credentials
20. What is an IVR (Interactive Voice Response) system? → An automated phone system that interacts with callers using voice prompts and keypad input
21. What does a regular audit of CDR (Call Detail Records) help a business administrator identify? → Unauthorized calls, toll fraud, billing errors, and unusual call patterns
22. Which combination of protocols provides the most complete protection against eavesdropping on VoIP calls? → TLS for SIP signaling combined with SRTP for media encryption
23. What is the primary security function of a Session Border Controller (SBC) in a VoIP environment? → To provide security, interoperability, and control at the border of a VoIP network
24. What is a codec in the context of VoIP? → A device that compresses and decompresses audio data
25. What is the best practice for maintaining IP phone firmware in a business environment? → Test new firmware on a small group of phones before deploying to the entire fleet
26. What quality issue occurs when VoIP packets arrive out of order? → Jitter
27. What is the main difference between an IP PBX and a traditional PBX? → IP PBX routes calls over an IP network instead of circuit-switched lines
28. What does the term 'extension' mean in a PBX context? → An internal phone number assigned to an employee or device within the PBX
29. What does E-911 compliance require of business VoIP phone systems? → The system must transmit accurate physical location data with every emergency call
30. How do malicious actors use SIP scanning against business phone systems? → To discover and exploit vulnerable VoIP devices or servers for toll fraud or eavesdropping