SIP and international calling guides
What SIP trunks are, how phone systems reach the phone network, and how to call any country well. Written to answer the question, not to sell you one.
Want an answer for your own numbers? Try our free SIP and VoIP tools.
All guides
Start with the one you came for.
What is a SIP trunk?
How a SIP trunk connects your phone system to every phone, how many channels you need, what it costs and how to keep it safe.
- How it works
- Channels
- SIP vs PRI
- Costs
- Security
- STIR/SHAKEN
- Choosing a provider
What is a virtual phone number?
How a number with no SIM or line behind it reaches you, the number types, free numbers and what virtual numbers cannot do.
- How it works
- DID numbers
- Local, mobile, toll-free
- Free numbers
- Limits
- Pricing models
SIP troubleshooting
A fault finder and one chapter per symptom: registration, failed calls, one-way audio, drops, call quality, keypad tones and caller ID.
- Fault finder
- SIP log
- Registration
- One-way audio
- Dropped calls
- SIP ALG
How much does an international call cost?
What each way of calling costs, why some countries cost more, who pays, and a calculator for your real bill. With E.164 format and a free number formatter.
- Ways to call
- Call cost calculator
- Why prices differ
- Who pays
- E.164 format
SIP trunk configuration
The four settings and one dial rule, shown where they go in 3CX, FreePBX, Asterisk and Yeastar.
- Settings
- Dial rule
- First call checks
- Errors
How to call any country
Country codes, how to dial from where you are, rates and the best time to call, for 25 countries.
- Country codes
- Dialling
- Rates
- Time zones