A SIM card is simply an "information chip" that programs your phone number and settings like your address book (if you stored them to your chip instead of to the phone's memory) from one phone to another.
SIM cards are usually transferable between any phone that is also GSM capable and is not "locked" to a different phone company than yours. I have transferred a SIM chip from a "uniband" (800 MHz) phone to a "dual band" (800 and 1900) and later to a tri-band (800, 900 and 1900) phone with no problems.
Good luck!
I just need to know something about moving this SIM to a better phone. Do I just need to make sure that a new phone has both 850 and 1900 frequencies? Will it not matter if the new phone supports other frequencies also? Thank-you.

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