Global Systems for Mobile (GSM) communication is a cellular network operating between 850-900MHz, or 1800-1900MHz frequency bands. Code division multiple access (CDMA) is a form of multiplexing and a method of multiple access that divides up a radio channel not by time (as in time division multiple access), nor by frequency (as in frequency-division multiple access), but instead by using different pseudo-random code sequences for each user. Coming to their history, the GSM was originated in Europe in the year 1990 and gained world wide popularity because of its modern network features which are available to the individual mobile phone user. CDMA was developed by Qualcomm Inc. and it became an international standard in 1995. GSM is a widely spread standard and CDMA is a patented technology. That is you must pay a royalty for using CDMA! Also GSM covers the entire Europe, Asia except Korea, Africa and Middle East. So being a GSM user one can have virtually an international roaming. You can easily use a GSM phone in any of these countries while roaming. In South America CDMA is generally 1900MHz, elsewhere generally 800MHz. Brazil seems to have nothing but 1800MHz GSM. In GSM phones, you can change the SIM card whereas in CDMA phones the SIM card is sealed.