I too will be after a SIM card when I'm in Hawaii later this year. I'm looking at going with T-Mobile and will set things up after I arrive in Hilo. I know where the store is located, so hopefully I'll be able to get someone to help me set things up.

At this stage I'm looking at a plan that I can add on the $10 international plan. The plan I'm looking at is between $50 and $70, just gotta decide which features of each I need.

Main uses will be internet (Facebook etc), maps and phone calls to home (though I'll use free wifi wherever possible).

I have an unlocked Telstra iPhone 4s.