GSM in Guam
We have experimental verification. GSM works on Guam, and roaming from NTT DoCoMo works properly. No GPRS (packet service), just basic voice service. And the GSM only works near the major tourist/population centers, not the remote south/east parts of the island.
The snorkeling, btw, was fantastic. We saw eels, triggerfish, wrasses, tangs, unicornfish, a few puffer-family fish, and some nice coral. Jealous yet :-)?
We met some guys from Wisconsin who were on a two-week diving trip to Truk and Palau. Man, if I did that and called home to Wisconsin where my wife was dealing with 30cm of snow and -19F (-28C) temperatures, when I got home the locks would be changed.