Originally Posted by
Henwurst
Yup, Guam is a US territory just like Puerto Rico.
Not just like. Puerto Rico is within the main US Customs and Immigration areas. That is, it's just like flying between US states when going to/from Puerto Rico and the mainland US - there are no passport or Customs checks because the rules are the same for both areas.
Guam has Customs completely independent of the federal government, and it's handled by local government officials and laws. Immigration in Guam is handled by the federal government, but has special rules. For example, there is a special Guam-only Visa Waiver Program that makes citizens of some countries eligible to visit Guam without a visa that would need a visa to go to the mainland US.
Hawaii has separate customs from mainland.
No, it does not. There's nothing different about Hawaii as far as Customs goes than any of the other 49 states. Hawaii does have special Agriculture rules at the federal level that are different from the mainland US. Among other things, there are certain fruits that you can bring with you on your person from Asia into Hawaii as an inbound passenger that are prohibited on the mainland, and you must pass through Agriculture (but not Customs or Immigration) inspection when flying from Hawaii to the mainland US.