Try to change his sitting arrangement so that he is isolated from his friends and keep the classroom discussion/work interesting and engaging. If the uncontrolled talking continues and is accomapnied by lack of focus, distractability, and inattention, you may need to talk to his parents and suggest an evaluation by his regular health care provider.
That's a tough one. Are you practicing at home for him to wait his turn? You could try that and using hand signals..but there has to be consequences when he does not stop and rewards for when he does. It's going to take a while and a lot of patience....but you need to keep working at it. Also if it is because he can not hear his teacher speaking you might want to get his hearing checked. If his interuptions are him asking questions about what is being discussed he could write those questions down instead of interrupting and then ask them when it is appropriate to ask them.