Twitter recently started rolling out the new Activity Stream to reveal more information about what the people you follow are doing on Twitter.
Now, users can have Twitter send them a SMS message to alert them when they have been followed, retweeted, or had a tweet favorited by another Twitter user, as reported on Mashable.
Setting up the alerts is simple, taking all of two steps--assuming you already have your wireless number linked to your Twitter account.
Log in to your Twitter account on Twitter.com, go to Settings and click on the Mobile tab.
If you don't have your wireless number linked to your Twitter account, you will be prompted to set it up. Provide your wireless number and then follow the instructions; it only takes a couple minutes to complete.
After you have your wireless number set up, or if you already had your number set up, under the Mobile tab you will see various options for SMS alerts to your device. The new notifications are located under Activity Notifications.
To turn on an alert, you only need to check the box next to the type of alert you would like to receive. If you turned on an alert for your tweets that get a favorite or retweeted, you will be able to narrow down to alerts only from people you follow, or from anyone.
To turn off any of the alerts, revisit the Mobile Settings page and uncheck the box next to the alert you wish to no longer receive.
Make sure to click on Save once you're done to save any changes you have made.