The difference between buying a SIM card and signing up for a mobile phone plan in the United States is as follows:
SIM card refers to a small chip that stores information about your mobile phone number and network subscription. You can buy a SIM card from a store or online, and then insert it into your phone to use the corresponding mobile network services. Buying a SIM card usually involves purchasing a pre-paid plan or a post-paid plan with a certain amount of data, minutes, and text messages.
Signing up for a mobile phone plan, on the other hand, typically involves signing a contract with a mobile phone company to receive monthly services such as voice, data, and text messaging. This usually requires personal information like name, address, and credit check. With a signed contract, you may be able to enjoy certain benefits like discounts on devices or additional services.
In short, the main difference lies in the fact that buying a SIM card is more flexible and involves less commitment while signing up for a mobile phone plan usually requires a contract and may offer more benefits.
In English, the difference can be explained as:
SIM Card: Purchasing a SIM card allows you to use mobile services by inserting it into your phone and selecting a pre-paid or post-paid plan.
Mobile Phone Plan: Signing up for a mobile phone plan involves signing a contract with a mobile company for monthly services with possible additional benefits like device discounts or extra services.