I have an iphone(firmware 1.0.2), which I have activated using an employer provided att sim card. If some time in the future if I switch employers and I want to sign up for a new att plan through iTunes(going through the Apple approved procedure), is it a matter of just reformatting the iPhone back to 1.0.2 and going through the activation once again and setting it up as a new account?

I have not jail broken or sim unlocked this phone, just a simple activation. I am not sure exactly what happens in the "Activation" procedure done through iNdependence, hence my questions.