GSM World <http://www.gsmworld.com> lists all countries and networks.
You can check networks for the countries to see which GSM they use.
As an example Anguilla uses GSM 850.  Antigua & Barbuda uses multiple
different networks i.e. 900/1900/850.  You'll have to do some footwork
to determine which Central American and South American countries use
different frequencies.

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Rogers Wireless  in Canada has 850 and 1900. Since it was a puppet of AT&T, it
announced its switch from TDMA to GSM at about the same time as AT&T, and thus
converted its 1900 to GSM first and now converting its 850 to GSM as well.

Il giorno Tue, 30 Mar 2004 09:35:07 -0600, X-Eliminator
<blablabla@aohell.com> con una bandiera della rinata Fiorentina in
mano e lo striscione "Meglio liberi all'inferno che schiavi in
paradiso" nell'altra cosi' parlo':