Don't mean to revive an old thread,

But I just had a similar conversation.

I was trying to redeem my 3 free days on National for an upcoming trip to Guam.

But the computer was not letting me redeem my free days in Guam, so I call National.

Me: Hi I would like to book a car in Guam, and use my 3 free rental days.
Agent: Okay, Guam?
Me: Yes, G-U-A-M
Agent: Guam International Airport?
Me: Yes
*Agent collects my information as to my date of arrival/departure*
Agent: Sorry sir, it appears that your free reward days can only be used in the US and Canada and is not valid on international rentals
Me: um...but Guam is part of the US
*silence for about 15 seconds*
Agent: Sorry?
Me: Guam is an US island in the South Pacific
*silence for another 10 seconds*
Me: Hello?
Agent: Sorry, it appears that we cant over-ride the system, and the free day is not valid in Guam
Me:...Thank you, have a good day

Looks like I might just have to pay for my rentals.
I am ES status with National, and just Gold with Hertz and no Status with Avis.
But I'm staying at the Hyatt, which has Hertz and Avis in the lobby...and would be more convenient for me to rent from either Hertz or Avis because of that....any idea who would have better cars? And would either offer an upgrade? I am going to book a Midsize, but would like an upgrade to at least a full size...or possibly even pay a small amount for a bump up to a Premium SUV

Thanks