Good morning Janice, if your physical phone does not support 4G and later there wont be much that can be done to add life into the device and keep it to make calls. In short, you will need to replace this phone and switch to a newer model. If you are unsure you can have someone look at the phone and can tell you specifics. Anything below iPhone 5 will need to be replaced or andriod phone made before 2011.
Unfortunately you will need a new phone as your old phone doesn't have the correct hardware to support 4G.
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