Sprint uses CDMA while AT&T & Cingular use GSM. GSM phones have SIM cards while CDMA phones don't. Sprint uses PCS because the 1900 MHZ frequency range is classified by the FCC (I believe it's the FCC) as PCS, regardless of digital standard. Sprint mainly operates in the 1900mhz (PCS) range on CDMA and AT&T & Cingular operate in the 1900mhz (PCS) on GSM. So the phones made for Sprint won't work with any GSM carrier.
I was curious if the phones sprint can be used on the cingular network, I thought that sprint was on the PCS newtork and AT&T/Cingular ran on GSM, wondering if the samsung phones that these two offer were interchangable assuming the phones were unlocked in between networks? Help please?

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