🙂 A SID, or system Id tells your phone what network it should use as its home system. This way the phone knows when it is roaming and what tower signal it should use. Commonly with CDMA phones A side systems end with an odd number (ie Alltel in Phoenix is 53) and B-sides with an even (Verizon is 48 in Phoenix). This number is put in your phone when programming your phone number.

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