Legal Question in Business Law in California

You can get a court order for almost anything, assuming the desired order involves the enforcement of a legally-recognized right you have against someone else. Needless to say, obtaining a court order involves making a convincing presentation to a court. More often than not, you'd have to start by filing and serving a lawsuit. This probably is going to be more expensive and troublesome than it's worth. However, if the cell phone number is that valuable, you can (perhaps) pursue the transfer in court.

I agree but also would interject that the person who has paid for the account is the "owner" and depending on your arrangement with then, may have a superior interest that may be more convincing. It may be possible that you pay all the costs and still lose.