Is it really an addiction and not a habit? It is hard to define simply because if smoking were an addiction, how does one explain away the fact that smokers can get a full 8 hours of sleep without the need to smoke (sure some exceptions)
There are smokers who light up as soon as they pick up the phone, start the car or open a beer. That's out of habit and not an addiction. The addiction part comes when the nicotine kicks in and demands a fix regardless of the phone, car or beer. It's both.
It depends on what you're smoking, If you're smoking 'Marijuana' it doesn't have any substances that can get you addicted, Although, you can be 'Mentally Addicted' which means that you Really like how it feels and therefore not want to stop. Even if you could stop.