It depends on the courthouse and courtroom. In California courts, state and federal, you do not have to take off your shoes unless they set off the alarm. You are allowed to bring your cellphone into every courtroom I've ever been in. However, it has to be turned off. I've seen judges issue steep sanctions for phones going off, and I know of one courtroom where the judge keeps a bucket of water by the bench; if a phone goes off, the bailiff collects it and "stores" it in the bucket of water. Some federal courts don't allow any electronics into the building without a court order (I've had to get one to bring a laptop in so I could do a trial).