Okay, I went to my service provider (Cingular) and they have a new plan that will work for us. It wasn't offered back when we got our new phones (Jan'04). It's a nationwide plan and it's $10/month more, but we'll get alot more for our money. There's 3 of us on our family share plan and with this new service, we'll be able to talk to each other anytime and it doesn't go against our minutes which by the way also increased. It also has the rollover feature for any unused minutes. So, ended up working out well. And, supposedly the entire island of Oahu is now covered by Cingular with the new technology GSM, whereas back in January'04, the island wasn't covered. Worked out good! Just thought I'd post this for any other Cingular customers who might be interested.
Aloha!

mlarson, since your free coverage is Nationwide, I would check on Hawaii before you rack up hundreds of minutes.

Yes, they are a part of our nation but geographically they are remote.

Yes, Hawai`i is included in Cingular's Nationwide coverage. I have been on a Nation plan from Cingular for a few years now, using L.A. service and numbers here on Maui.

Cingular itself does not have service in Hawai`i right now. You will be roaming on AT&T's network, or in some places, T-Mobile. AT&T has claimed to have full coverage since their GSM rollout in 2001, but as with any service, there will be dead areas.

I'm thinking of switching to T-Mobile and will be using the phone on our trip to Oahu and Kauai in August. Think we'll have trouble using T-Mobile there?

Cingular gave me a map of entire US which included both Hawaii and Alaska. THe entire island of Oahu is covered (per the map key) and parts of THe Big Island. So, yes it should be okay.

Anyone know if Sprint includes Hawaii in their coverage? I didn't see it in the map on the website (not even for roaming!), so I'm guessing it isn't

Yes, if your phone works in the US, it will work in HI. Here is Sprint's service map for Hawai`i.
http://makeashorterlink.com/?N17E22868. If your carrier does not have service in HI, you can still roam on another carrier.