Finally now you didn't need any Google+ invitation just to join the new social network by google. After about 90 days can only be used for a limited circle, Google's social networking site finally opened to all freely. Now we can easily join a google+ social network without an invitation keys.

Beside opening the access of google+ to all, there's several other new features on this google social network sites such as a search and improved Hangouts.

Other Google+ mobile improvements include better Short Message Service (SMS) support, allowing users in the U.S. and India to post to Google+, receive notifications and respond to group messages via SMS; improved +mentions support to let +[insert name] inside a post or comment to add users to a conversation; and the ability "to +1" comments from Google+ (for iOS but not yet for Android)

you can find a further news and information about Google+ finally open for all on eweek.com here.