Google plans to open up Gmail, its free e-mail service, to everyone worldwide. Initially, Gmail was an exclusive club — an invitation from another Gmail user was required. In August 2005, Google opened Gmail up to those willing to submit a mobile phone number as a means of identity verification and as a way to limit the number of accounts spammers might be able to abuse. Such concerns no longer appear to be an issue. Last week, Google removed the phone number requirement in Africa, Brazil, Europe, and the Middle East. It remained in place in Asia, North America, and most of South America until today. Would-be Gmail users in other countries, including Australia, Japan, and New Zealand, have been able to sign up for the service without a phone number since last summer. Google claims to have “tens of millions” of Gmail users, significantly fewer than the free e-mail services offered by Microsoft and Yahoo.