To receive SMS (text) notifications when important Google+ events--like when something is shared with you--occur:
- Sign in to Google+ .
- Click your full name or email address in the Google bar.
- Click Account settings.
- Click Google+.
- Click Add phone number.
- Click Send verification code to verify you entered your phone number correctly.
- Enter the verification code and click Save.
- Select the notifications you want to receive via SMS.