If you have ever used iMessage on your Mac to send a message to an iPhone the recipient will tell you just how frustrating it is flicking between two message streams.. When you send from your mac, by default it will send from your Apple ID (email address) and not your phone number. Which means the recipient may end up with two separate conversation threads.
Not anymore.. All you need to do is ensure your iPhone is running iOS 6, and your Mac is running OS X 10.8.2.
Launch iMessage on your Mac, navigate to iMessage preferences and then over to the Accounts tab. Now click to add an email address. In the box provided enter your mobile number minus the first 0, now press the tab key on your keyboard. You should see a message pop up suggesting iMessage is going to send an email to the number you have enter. Click to accept the message. Now on your iPhone goto Settings > Messages, and slide iMessage off. Now exit the settings menu. Return to Settings > Messages iPhone and slick iMessage back on. Exit the settings menu and now restart iMessage on your Mac. You should now be greeted with a message explaining your number will now be used to receive iMessages.
Now if you want, you can also set iMessage to also send from your email address, back in preferences under the accounts tab, select your number from the drop down at the bottom of the settings form.