Some North American GSM phones can do 800 or 1800, but most can't.
North American GSM phones cannot do GSM 1800 only GSM "850" or GSM
1900. GSM 1800 is a Euro-Asian frequency. And before anyone gets upset GSM 800 is the same thing as GSM 850. For some reason unknown to me when GSM was introduced to use on cellular networks it was decided to call it GSM 850 even though it uses the same transmit and receive frequencies as other cellular technologies such as CDMA or TDMA (IS-136.)