By Rob Lumley
If you have OS X Mountain Lion v10.8.2 or later, and you have a phone number associated with your Apple ID, it is automatically added to the list. When you set up your iPhone with iOS 6 or later installed to use an Apple ID, your phone number is associated with your Apple ID.
appleid.apple.com is where you login and verify your mobile number is associated with your Apple ID. Please select Phone Numbers in the left column and use your cell phone number in the mobile number field.
Click Save Changes.
Once that has been saved, when you open the preferences to Messages on your Mac, you will see your number in the drop down list for starting new conversations from the number instead of email.
Once you make this selection, you should receive a message on your iPhone to allow the number to be used from your Mac.
Now all iMessages sent to and from your iPhone’s phone number will be synced on your Mac.
Let me know if you have problems.