Sleeping thru important phone calls

First and foremost, overtime is mandatory. Its in my contract that everyday I'm scheduled to work I'm subject to get called in. I only say that because I posted in another group and everyone said I'm stupid for answering my phone even though I explained it's not optional. Please don't give me shit for it, its part of my job. Anyways, I just hit my 90 days last week meaning I'm eligible for overtime. Overtime goes based on senority, I have the least so if everyone else passes i have to take it. Even if I stay over til 3am, if they need someone in at 11am I'm stuck taking it. Friday and Saturday I worked 3pm to 3am, Sunday morning I slept right thru the phone call to come in early. Thank God they called back the person above me and he came in otherwise I would've gotten a point. My ringer was turned all the way up, and I've since turned up the vibrate when ringing. Staying up isn't an option for me. Friday and Saturday nights I didn't get home til after 4 am because we had an ice storm, and I didn't fall asleep til after 5. How do yall make sure you wake up for important phone calls? Are there certain ringtones that work for you? Should I ask if my foreman can put a note next to my number to call back to back? I love my job and I love overtime, it's just a bitch to wake me up sometimes. Thanks!