The signature test isn't exactly phoning home, but it isn't letting the user choose to whether to allow the test to connect to some website. This is always bad. The Module::Build signature test contains

skip_test("Skipping unless \$ENV{TEST_SIGNATURE} is true") unless $ENV
+{TEST_SIGNATURE};
[download]

which is the way it should be done. libwww-perl's Makefile.PL opens a socket to google.com (as a way of detecting a live connection), and if successful, prompts the user to run some tests that tries to access some sites , which while not ideal, is better than blindly connecting to whatever server to do anything without letting the user choose.

The user should always be prompted, and the default should always be to not connect, even if the entire purpose of a distribution is to interface to a specific remote server (like WWW-Yahoo-Groups ...).