Google has opened up its Google Voice service to the broader public, dropping the requirement for an invitation to use the service. The service still remains available only in the US. Launched over a year ago, Google Voice has already more than 1 million users, Google said. Google Voice allows for the integration of multiple lines and voicemail accounts on one number, and includes features such as low-cost VoIP calls, SMS-to-email, voice transcription, conference calls, call blocking and a mobile app.