Glossary
Phone Number and VoIP Glossary
Plain-English definitions of the terms that come up when choosing a phone number, from DialAnyone. Each entry stands on its own — no prior term required.
No jargon · Each definition stands alone
At a glance
14
- Terms defined
- 14
- With links
- 8
Virtual phone number
A phone number that lives in an online account rather than on a SIM card. Calls and texts are delivered over the internet, so the number works from a browser or an app in any country. It is a real, dialable number on the public telephone network — the difference is where it terminates, not what it is.
DID (Direct Inward Dialing)
The telecoms term for a phone number that routes an inbound call to a specific destination without an operator. Virtual number providers buy DIDs from carriers and assign them to accounts. When a provider says "DID availability", they mean which numbers they can currently sell.
VoIP (Voice over IP)
Carrying a phone call as data over an internet connection instead of over a traditional circuit. VoIP is why an international call can cost cents rather than dollars. Some services block VoIP numbers for verification as an anti-fraud measure, which is why code delivery is never guaranteed for every sender.
WebRTC
The browser technology that lets a web page place and receive real-time audio calls without a plugin or a downloaded app. It is what allows a call to run inside a browser tab.
OTP (one-time passcode)
A short numeric code sent by SMS to confirm you control a phone number. Receiving one requires a number that supports SMS — which most countries’ virtual numbers do not. A voice-only number will never receive an OTP.
Voice-only number
A phone number that can make and receive calls but cannot send or receive text messages. This is the norm rather than the exception for virtual numbers: SMS support depends on the local carrier and regulator, and in most countries it is unavailable to any provider.
A2P 10DLC
The US registration regime for application-to-person messaging sent from ordinary 10-digit long codes. Businesses sending automated SMS to US numbers must register a brand and campaign with the carriers. Person-to-person conversational texting is treated differently.
Country calling code
The prefix that identifies a country on the international telephone network, written with a plus sign — +44 for the United Kingdom, +81 for Japan. Dialing internationally means replacing the plus with your own exit code, such as 011 from the US or 00 from most of Europe.
Area code
The three-digit prefix after +1 that identifies a region within the North American Numbering Plan. Newer codes are usually added as overlays covering the same geography as an existing code rather than by splitting a region, so two neighbours can hold different area codes.
NANP (North American Numbering Plan)
The shared numbering system covering the United States, Canada, Puerto Rico, the US Virgin Islands and much of the Caribbean, all reachable under the +1 country code. Membership is why a call from the US to Canada dials like a domestic call.
eSIM
An embedded SIM profile downloaded to a device instead of inserted as a plastic card. It provides mobile data on a local network without swapping hardware, which is what makes it useful for travel.
Number porting
Moving an existing phone number from one provider to another while keeping the number itself. Porting is a regulated process, takes days rather than minutes, and requires proof that you control the number.
Caller ID
The number shown to the person you are calling. With a virtual number you can present your virtual number rather than the underlying line, which is how a call placed from abroad can appear to come from a local number.
Toll-free number
A number where the recipient rather than the caller pays for the call, identified in North America by codes such as 800, 833, 844, 855, 866, 877 and 888. Toll-free numbers are national rather than tied to a city.