This PHP library makes it easy to work with the SendGrid Subuser API. It was made to scratch our own itch, and as such it currently only implements the parts of the API that we needed. Please feel free to request additional features or send pull requests.
$sendgrid = new SendGrid\Api("my_username", "my_password");
// Create a new sub user
$user = new SendGrid\SubUser("wanted_username", "password",
"[email protected]", "email.domain.example.com");
$sendgrid->addSubUser($user);
// Retrieve existing sub user
$other = $sendgrid->getSubUser("sub_username");
// Assign IPs to a user
$other->assignIps(array("1.2.3.4"));
See example/example.php for more examples.