I don't think it is unethical. If they came back and offered all the customer's who switched 2 years free to switch back, after you were out of pocket for serv

I don't think it is unethical. If they came back and offered all the customer's who switched 2 years free to switch back, after you were out of pocket for serving them for a year free, would you feel unfairly treated ? Inducing people to break a contract seems to me to be going a step further, but even then I would say it depends on the details. Inducing someone to break an abusive cell phone or ISP contract doesn't bother me. Inducing someone to break a maintainance contract with an individual, say an independent plumber, would probably be wrong.