Frequently Asked Questions (FAQ)

Validation and types of numbers

What is the difference between isPossibleNumber and isValidNumber?

To understand the behavior of functions, please refer to the documentation in the Javadoc/C++ header files. For example, see isPossibleNumberWithReason in PhoneNumberUtil.

Why does PhoneNumberUtil return false for valid short numbers?

Short numbers are out of scope of PhoneNumberUtil. For short numbers, use ShortNumberInfo.

What does it mean for a phone number to be valid?

Our phone number library can tell that a number range is valid when there is sufficient official documentation, with some latency after this fact is brought to our attention via issue reports or notifications (see below for more information on where our metadata comes from). A valid number range is one from which numbers can be freely assigned by carriers to users.

Do not rely on libphonenumber to determine whether numbers are currently assigned to a specific user and reachable. Some products (e.g. Google 2-step verification) do this with a verification step e.g. by sending an SMS or placing an automated phone call with a verification code). This is not technically feasible without such a verification step given the complicated international world we live in, with varying standardization practices in different regions.

When should I use isValidNumberForRegion?

Rarely! Many people have phone numbers that do not belong to the country they live in. This applies particularly to mobile numbers, but may also be true for VoIP numbers etc. Note also that the regions your application supports may not be the same as the regions we support. For example, the Channel Islands such as "Jersey" have their own region code - JE. If you allow these users to sign up as a British user ("GB"), their phone numbers will not be considered valid for the region "JE".

One use-case where this method may be useful is if you want to see if a FIXED_LINE number for a business matches the country it is in, to try and spot data errors.

What types of phone numbers can SMSs be sent to?

SMSs can be sent to TYPE_MOBILE or TYPE_FIXED_LINE_OR_MOBILE numbers. However, in some countries it is possible to configure other types, such as normal land-lines, to receive SMSs.

Why did I get TYPE_FIXED_LINE_OR_MOBILE as the type of my phone number?

Some number ranges are explicitly defined as being for fixed-line or mobile phones. We even represent ranges defined as being "Mostly land-line" in this way.

What about M2M (machine to machine) numbers?

libphonenumber does not support M2M numbers at the moment, but might in the future.

One of the reasons libphonenumber doesn't support M2M so far is because no one could explain their use to us sufficiently.

We don't require that a number to be supported by the library has a human at the other end since we already accept premium rate services and they might go to an automated system instead. But to date we only accept ranges that a human might call or send an SMS to.

M2M numbers would violate this assumption and we'd have to evaluate the consequences for existing APIs and clients if M2M numbers would be considered valid by the library.

Many people use this library for formatting the numbers of their contacts, for allowing people to sign up for services, for working out how to dial someone in a different country, for working out what kind of cost might be associated with a number in an advert, etc. We don't think the lack of M2M support hinders any of those use-case, but we might be wrong.

If you would like libphonenumber to support M2M numbers, please engage with the developer community at Support M2M numbers #680 with further information to address our questions and concerns and please describe what kinds of use-cases fail because M2M numbers are not supported by the library.

More information on this issue would be very welcomed!

Related issues: Support M2M numbers #680, #930: JTGlobal - an MNO based in the UK, #976: Norway, #985: South Africa, Vodacom, #910: Sweden, #657: Canada, #550: Belgium, #351: Norway, #332: Netherlands

Representation

What is the maximum and minimum length of a phone number?

We support parsing and storing numbers from a minimum length of two digits to a maximum length of 17 digits currently (excluding country calling code). The ITU standard says the national significant number should not be longer than fifteen digits, but empirically this has been proven not to be followed by all countries.

Formatting

Can / should we format phone numbers in a language-specific way?

No, phone number formatting is country-specific and language-independent. E.g. formatting a US number in a French way (e.g. the way a France number is formatted) for a French user is undefined and wrong.

It is true that in some countries phone numbers are typically written using native, not ASCII, digits; our phone number library supports parsing these but doesn't support it at formatting time at the moment.

Why does formatNumberForMobileDialing return an empty string for my number?

If we don't think we can guarantee that the number is diallable from the user's mobile phone, we won't return anything. This means that for numbers that we don't think are internationally diallable, if the user is outside the country we will return an empty string. Similarly, in Brazil a carrier code is essential for dialling long-distance domestically. If none has been provided at parsing time then we will return an empty string. If you get an empty string and are okay providing a number that may not be diallable, you can call another of our formatting numbers instead.

Metadata

Where do we get information from to determine if a number range is valid?

In theory, phone numbering plans are all supposed to be administered through the ITU. Many countries' phone numbering plans may be found on the ITU website.

We receive automatic notifications when a new ITU plan has been filed, which may or may not be before it comes into effect.

Not every country files their numbering plans with the ITU nor are the plans filed with ITU always up to date. In some countries, the numbering plans are directly handled by a government authority, while in others, most of the work is done by telecom companies (the government's role being only to distribute ranges at the prefix level, with the actual partitioning within the prefix done by the telecom).

A large part of the data in PhoneNumberMetadata.xml comes from the ITU documents, but because they're sometimes insufficient, we also include data from other sources, including user bug reports, telecom company home pages and government telecommunication authorities.

There is no RFC indicating where the data comes from, or what format they're in.

We'd love to consume machine-readable numbering plan data (assigned ranges, carrier & geo mappings). If you can connect us with partners in the industry to achieve this, please do so. Thanks!