If you have an Android phone registered with Google services, Google has matched your phone number to your Google Plus profile and plans to turn the association into yet another de-anonymizing tool.
All phones have caller ID. But in 2014, Google is extending caller identification on Android phones to access Google Plus profiles and show Plus profile pictures and names to anyone making or receiving calls on Android phones.
If you have registered a phone number with Google, it appears that you have already "opted in."
Much like with tying Plus "real name" profiles to Play Store and YouTube comments, Google is keen to remove the anonymity from making and receiving phone calls.
Google Plus profiles require people to use their real name, a policy that Google strongly enforces, even up to the point of having users send in government-issued ID. Users can then add a nickname or "other name" if it is within Google's strict "real name" guidelines.
So when a random person calls you, they will see your Plus photo and your real name, thus making it easier to find your profile on Google Plus.
When you call people, you'll be able to see their photo and name as well.
Google's "Smarter Caller ID" comes as part of Android 4.4 KitKat, and you do not need to be in someone's address book for them to get your Plus name and profile pic when calls are made or received.
Google engineer Attila Bodis wrote,
Coming in early 2014, users who have verified their phone number and have discovery turned on will have their names and Google Profile photos display whenever they call you, or you call them (it’s great if a new friend who hasn’t been saved in your contacts yet calls you).
Check your Google Account to make sure you are happy with how you appear on caller ID by Google: http://goo.gl/g9P3Bp [https://www.google.com/settings/phone]
People who prefer privacy and at-risk populations (such as women) probably won't think it's "great" if strangers can call their number and instantly get their name, photo and the social network to find them on.
If you don't want random callers to see what you look like, to know your real name or alias, or know how to find your profile on Google Plus, you won't want this change to take you by surprise.
If you don't want Google's [Plus] Smarter Caller ID, visit https://www.google.com/settings/phone and un-check the box next to your phone number (or numbers).
There is currently no way to remove a phone number once it is registered with Google.