As a personal trainer I must say that soda is one of the key ingredients to keeping me in business!

Make sure you offset this with lots of pizza and an occasional jelly roll and I'll cut you a good deal on some sessions!

Seriously...
If you have withdrawal symptoms get some carbonated water and squeeze some fruit into it for flavor and you will do fine!
Soda with it's "liquid candy" ingredients has a dehydrating component that keeps you thirsty the more you drink it so it can be sort of a pseudo additive thing that is never mentioned in the soda commercials!
Avoid parties if you can because old habits die hard and drink plenty of water... That means that the money you would have spent on soda should go to bottled water just to have something to hold in your hand (It's a psychological thing trust me).
If you can get a juice machine which gives you a more natural sugar water from fruit and vegetables but do not live exclusively by this for sugar is still sugar even if it is not the processed kind like soda has... A blender will keep the fiber along with the juice so get one of those two and moderate between them.
And... If you ever slip back don't condemn and judge yourself you are only human but your body will thank and reward you for the effort to at least try to do better and in time you will be so purged from this subtle narcotic that you will feel more refreshed, energetic and cleansed.
Now get down and give me 50 push ups... What, you thought that was the end of it?

Hit a couple of laps around the forum too to get the metabolism flowing to help the cleansing process!
Stay Strong... Stay Positive... Good Luck!