What was announced in 2007 is now finished. NTT DoCoMo and AT&T announced today that the extension of a third-generation (3G) mobile network to all principal islands in the U.S. state of Hawaii has been completed.

Using AT&T's 3G network, which is based on W-CDMA technology, DOCOMO customers now have access to data and voice roaming services in the main populated areas of Oahu, Hawaii, Maui, Lanai, Molokai, and Kauai.

NTT DOCOMO began providing 3G roaming services on Oahu in October 2007 and then extended the services to other islands including Hawaii and Maui islands as the network was expanded.

DOCOMO handsets compatible with international roaming services in the Hawaiian Islands are the SH905iTV, SH906i, F906i, SO906i, N906iμ, SH906iTV, NM705i, NM706i (to be available soon), hTc Z, and HT1100.
Via this DoCoMo announcement.