What is a month-to-month SIM only plan?

A SIM only plan is a type of postpaid phone plan that offers features such as talk and text and data benefits but does not include a phone. SIM only plans are also referred to as a BYO (bring your own) phone plan, which do not have a lock in contract, meaning you can cancel anytime. With a SIM only plan, you receive either a SIM card or eSIM.