Yes, it's possible to move your number to a prepaid account. You just have to call Prepaid Customer Service (the number can be found at the "Contact Us" link in blue at the top right of this page) and make the switch.
If you want to use a daily prepaid plan, only "feature" type phones that do not require a data package will be compatible. You can check about your specific model with the Prepaid CSR when you call.
The main difference is that you must pay in advance for prepaid service, and with the daily plans, you only pay for the days you make calls on your phone.