Short answers to the specific questions that come up while configuring a trunk, testing a route, or sizing a deployment. Each one is deliberately one or two sentences. Where a topic needs more room, the longer treatment is linked from the section.
For the broader buyer questions see the business VoIP FAQ; for terminology see the glossary.
Connecting and authentication
Can one SIP account be used on several devices?
Sometimes, but the account may limit simultaneous registrations or calls. For stable business use, assign separate extensions where possible.
What is the difference between SIP registration and IP authentication?
Registration uses credentials and works well for changing internet addresses. IP authentication trusts traffic from approved fixed public IPs and is common for PBX or dialer trunks.
Do I need a static IP for VoIP?
A static IP is helpful for IP-authenticated trunks and firewall rules. A registered softphone can normally work on a changing IP if NAT is handled correctly.
What is IP whitelisting?
It is a security rule that accepts signaling or portal access only from approved IP addresses.
Which port does SIP use?
SIP commonly uses port 5060 for unencrypted traffic and 5061 for TLS, but providers may use different ports. RTP audio normally uses a separate port range.
Audio, media and devices
Why can I hear the other person but they cannot hear me?
One-way audio is usually caused by NAT, firewall, incorrect SDP addresses, blocked RTP ports, or a misbehaving SIP ALG.
Why does the call connect with no audio?
The signaling path may be working while RTP media is blocked or sent to the wrong address. Check firewall rules, NAT, codec agreement, and media IP settings.
Does VoIP work through a VPN?
It can, but the VPN may add latency, reduce available bandwidth, or alter NAT behavior. Test voice quality and routing before deploying it widely.
Can VoIP carry keypad tones?
Yes. Both sides must agree on a compatible DTMF method so IVR menus and PIN entry work reliably.
Can I use a fax machine with VoIP?
It may work through an ATA or T.38-capable gateway, but fax is less tolerant of packet loss and timing problems than voice. Email-to-fax is often simpler.
Can I keep using an old analog phone?
Yes, with a compatible ATA that supplies the analog interface and converts the audio to VoIP.
Numbers and porting
Can I keep my existing business number?
Number porting may be available when the current carrier, number type, country, and documents meet the receiving provider’s requirements.
What documents are needed for a virtual number?
Requirements vary by country and number type. They may include identity proof, business registration, address evidence, and a description of the intended use.
Are virtual numbers activated instantly?
Some are provisioned quickly, while regulated destinations require document review or local-address checks. Activation should never be promised before eligibility is confirmed.
What is the difference between local, mobile, and toll-free numbers?
A local number uses a geographic area code, a mobile number belongs to a mobile range, and a toll-free number lets eligible callers reach the business without paying the normal call charge.
Call handling and routing
Can calls follow business hours?
Yes. Time-based routing can send calls to teams during open hours and to voicemail, an on-call person, or another message after hours.
Can holiday schedules be configured?
A PBX can apply special greetings and routing rules for holidays or non-working days.
What is the difference between a ring group and a queue?
A ring group alerts selected users together or in sequence. A queue holds callers and distributes them as agents become available.
What is the difference between warm and blind transfer?
A warm transfer lets the agent brief the recipient first. A blind transfer sends the caller immediately without that private conversation.
Can supervisors listen to live calls?
Authorized monitoring, whisper, and barge features may be available. They should be controlled by role permissions and used according to recording and privacy laws.
Capacity, channels and billing
How many calls can one trunk carry?
It depends on the purchased channel limit, CPS limit, server capacity, carrier policy, and available bandwidth.
What does a 20-channel trunk mean?
It generally allows twenty simultaneous call legs. Conferences, transfers, and call forwarding can consume capacity differently, so real usage should be tested.
Why does CPS matter for a dialer?
CPS controls how quickly new attempts can be launched. Exceeding the limit may cause rejections, congestion, or carrier action.
What does 60/1 billing mean?
The first sixty seconds are charged in full; after that, usage is billed in one-second increments.
Rates and route quality
Can international rates change?
Yes. Wholesale carrier prices and surcharges can change. The effective date and notice process should be stated in the service terms.
Does the cheapest route always save money?
No. Poor answer rates, long delay, false answers, and weak audio can reduce productivity and create more redials than a better-quality route.
Is a high ASR always proof of a good route?
Not by itself. ASR changes with list quality, time of day, destination behavior, and how the network handles voicemail or announcements.
What does ACD reveal about traffic?
Average call duration helps identify whether answered calls remain connected long enough to match the expected use case. Very short ACD may indicate list, routing, or answer-supervision issues.
What is an acceptable PDD?
Lower is usually better, but normal delay differs by country and network. Compare routes under the same destination and testing conditions.
How can I detect false answer supervision?
Test known ringing, busy, invalid, and unanswered numbers while checking when billing begins and what SIP response or answer signal is returned.
Should I test more than one network in a country?
Yes. Landline and mobile operators can behave differently, and one carrier may perform well while another has poor completion or caller-ID support.
Why must numbers use international format?
Consistent E.164-style formatting lets the dial plan match country and network prefixes correctly and reduces failed calls caused by local trunk codes.
Can a route support verified caller ID?
Only when the number is authorized, correctly formatted, supported by the carrier, and permitted by the destination. Display can still vary at the receiving network.
Servers, security and data
Can a backup carrier take over automatically?
Yes. Failover rules can retry an eligible route after selected errors, but they must avoid loops, duplicate calls, and unexpected pricing.
What should a VoIP server backup include?
Back up configuration, rate tables, customer data, CDRs, recordings where required, encryption keys, licenses, and database state. Test restoration regularly.
Does a firewall alone secure a VoIP server?
No. Strong credentials, IP restrictions, patching, monitoring, fraud limits, access control, and backups are also necessary.
What does an SBC add to a deployment?
An SBC can protect the network edge, normalize SIP, manage NAT, hide internal addresses, enforce policy, and control media paths.
How long should CDRs be retained?
Retention should follow operational needs, contracts, tax rules, privacy law, and dispute windows. Keep only what is justified and protect access.
Can call recordings be stored outside the PBX?
Many platforms can export or archive recordings to approved storage. Encryption, permissions, retention, consent, and deletion policies remain important.
Integrations, remote work and continuity
Can VoIP connect to a CRM?
Yes. Common integrations support click-to-call, screen pop, automatic activity logging, contact sync, notes, and workflow triggers.
What can a webhook do in a phone system?
A webhook can notify another system when events occur, such as call created, answered, missed, completed, or recording ready.
Can remote agents use the same company number?
Yes. Agents can work through approved apps, IP phones, browser clients, or forwarded calls while the PBX keeps business routing and reporting centralized.
How do I estimate internet capacity for agents?
Add the expected bandwidth per call in both directions, multiply by peak concurrent calls, and leave additional headroom for signaling, other applications, and network variation.
What happens when the office internet fails?
Calls may stop reaching local devices unless failover sends them to mobile users, another site, voicemail, or a backup connection.
Does internet calling automatically include emergency service?
No. Emergency-calling support depends on the provider, number, registered location, device, and country. The service must be confirmed before relying on it.
Need a definite answer for your account?
Availability, caller ID behaviour, billing increments and emergency-calling support vary by destination and route. Ask sales with your destination list and we will confirm what applies to you in writing.