I am "on call" and thus have been provided with a company cell phone. This on call status is a condition of my employment and I am not paid any additional amount, but am entitled to bill the company if I am called upon to physically return to the office outside of my regular working hours.

If you are not classified as on call, and it is not a condition of your employment, you are not legally required to answer the phone. If you bring that up to them, they may make being on call a condition of your employment. At that time, you will either be required to acknowledge that and accept it, or disagree and risk being dismissed (if they wanna be spiteful). That having been said, you are probably in violation of the company policy for cell phone usage. It is, after all, company equipment and should not be used to conduct personal business any more than using a personal cell phone during company time is.

I have a pretty strict contract, and even I don't have any indication that management is entitled to come to my house!

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Though I am different from you,
We were born involved in one another.

For it was not into my ear you whispered, but into my heart. It was not my lips you kissed, but my soul.

Complete surrender should not just come at moments in which one faces overwhelming odds, but in the calm when it seems one is personally in complete control of one's life.