If you are flying hobby, that's the rule if you are within 5 miles. And remember that if the airport has a tower, you are to contact both the airport manager and the tower. I suspect that, like most of us, you will have a hard time getting hold of anyone at those heliports. Just take a bit, call the numbers and if someone answers, let them know that you will be flying, ingenral where and when. If no one answers, I would just make a note that you called and then go on. Might try calling the day before, just sit down and make all the calls in one session. Some, like the Santa Monica airport, might want you to call just before flying so just play nice with them. Bigger problem might be dealing with any local ordinances prohibiting flying!