View this page "GSM GPRS Module C1S"

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C1S is a small, light weight and low power consumption module that
enables digital communications services on GSM/GPRS networks for
machine to machine or user to user or user to machine wireless
applications.

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The C1S module implements a dual-band MS; it can be configured to
operate in the frequency bands either EGSM 900
MHz, and DCS 1800 MHz (European bands) or GSM 850 MHz and PCS 1900 MHz
(America bands).