Google Inc.’s e-mail service is almost ready to accept all comers, nearly three years after the online search leader shook up webmail companies by offering users an unprecedented amount of free storage and displaying ads based on the content of the correspondence.

From today, the company has removed the invitation-only restrictions on its Gmail service in Europe, the Middle East, Africa and Brazil. Google opened up the service last year in several other parts of the world, including Japan, Australia, New Zealand, Russia and Egypt.

Invitations to open a Gmail account are still required in North America, Asia and mostparts of the South America, but Google spokeswoman Courtney Hohne said those restrictions will be lifted very soon. Even then, Gmail will retain a ‘beta’ tag to signify that the company still considers the service to be in a testing phase.

Getting a Gmail invitation hasn’t been too difficult for some time. Account holders have had as many as 100 invitations to send out to friends and family. Anyone willing to provide Google with his or her mobile phone number can also request an invitation.

The invitations were prized commodities when Google first introduced the service in April 2004. Shortly after Gmail’s debut, some invitations were being offered on eBay for more than $100.

The reason for its popularity was the gigabyte of free storage it offered account holders – 250 to 500 times more than Yahoo! and Hotmail.

After those rivals boosted their e-mail storage to match Gmail, Google quickly upped the ante and now provides at least 2.6 gigabytes of free storage. The service still remains along way behind its two main rivals.