My employer requires us to carry a cell phone after hours after I have already worked my 40 hours without overtime pay.

I have been working for a company that requires us to carry a cell phone after our normal work day and all weekend. This is every 6 weeks and totals over 100 hours that we are required to work if called. In the past we have received some days off and some overtime pay. But recently I have been informed that no overtime will be paid for compensation. I have questioned the legality of this practice for awhile but as the economy grows worse I fear I will be terminated if I do not do as instructed. I am not up to date on the current rules and regulations for compensation to employees who work over a 40 hour week. I am not a salaried employee. What rights do I have if any if I