I have T-Mobile with tri band phones and
did not have any signal in Koror.
T-mobile confirmed they have no service there.
Most hotels seem to have wireless
internet in their lobby, bar or resturaunt areas.
I didn't use it in PPR, but in PHP it was
excruciatingly slow - Shared Dial-up speed.
Keep in mind that there is no high-speed
internet service in Palu, at least not for
the locals. It's still dial-up through palaunet.com
There may be pockets of cable-internet, but that
is still way too expensive for most people to afford.
There are internet cafe's around Koror, but I didn't experience them myself.
I just got back from ten days in palau, I used the internet in PHP one time to send out an email.
After that I used a calling card on a hotel lobby phone to call home and friends, that seemed to be the most economical and convenient way to reach the states.
Please Let us know how your trip went.