I updated my number on Google+, but that's not displayed in my friends' phone or their Google Contacts. It appears when they see my Google+ profile, though.
Your numbers are not synced to Google Contacts. Your friends need to install the official Google+ app in order to see your numbers.
Other users' address books are not synced with your G+ profile AFAIK. Your friends would have to either manually update their Google account contacts on the web or manually update their address book on their phone. Either way, if sync is turned on for that account on a friend's phone, updating the one will update the other.