phonenumbers 
golang port of Google's libphonenumber, forked from libphonenumber from ttacon which in turn is a port of the original Java library.
You can see a live demo of the number parsing of the master branch of this library at https://phonenumbers.temba.io/ Compare results with the official Google Java version.
This fork fixes quite a few bugs and more closely follows the official Java implementation. It also adds the buildmetadata cmd to allow for rebuilding the metadata protocol buffers, country code to region maps and timezone prefix maps. We keep this library up to date with the upstream Google repo as metadata changes take place, usually no more than a few days behind official Google releases.
This library is used daily in production for parsing and validation of numbers across the world, so is well maintained. Please open an issue if you encounter any problems, we'll do our best to address them.
Version Numbers
As we don't want to bump our major semantic version number in step with the upstream library, we use independent version numbers than the Google libphonenumber repo. The release notes will mention what version of the metadata a release was built against.
Usage
// parse our phone number
num, err := phonenumbers.Parse("6502530000", "US")
// format it using national format
formattedNum := phonenumbers.Format(num, phonenumbers.NATIONAL)
Rebuilding Metadata and Maps
The buildmetadata command will fetch the latest XML file from the official Google repo and rebuild the go source files containing all the territory metadata, timezone and region maps. (you will need svn installed on your path)
It will rebuild the following files:
metadata_bin.go - contains the protocol buffer definitions for all the various formats across countries etc..
countrycode_to_region_bin.go - contains the information needed to map a contrycode to a region
prefix_to_carrier_bin.go - contains the information needed to map a phone number prefix to a carrier
prefix_to_geocoding_bin.go - contains the information needed to map a phone number prefix to a city or region
prefix_to_timezone_bin.go - contains the information needed to map a phone number prefix to a city or region
% cd cmd/buildmetadata && go install . && cd -
% $GOPATH/bin/buildmetadata