I still remember this cool feature put out by Google in Gmail Labs last year wherein you can unsend an email message when you accidentally hit the send button to quickly only to realize after a few seconds that you should have not send it yet. Well, if you thought that was cool then, it becomes even cooler now as Google does the same with your Gmail Contacts.
Google has added this feature to Google Contacts, allowing you to revert your contact list and undo any mistakes made up to 30 days in the past. So when you accidentally deleted a contact data from your Gmail account while say, synching your account with another device, you can simply restore these contact data by simply going to your Gmail’s Contacts section and selecting “restore contacts” from the more actions options.
And that’s it. Contact data that you have deleted will become part of your active Gmail Contacts again and will be restored exactly the same when you deleted it. There’s one more point to note here. If you have restored Contacts data, contacts that were not on the list when you deleted the data will be deleted once you’ve restored your original contact data. The good news is that you can always restore these contact data anytime.
Read [Gmail Blog]