Pre-paid internet cards/services???? Do you know any?
 

is there any paid internet card service to use when traveling?

This European friend of mine is going to Hawaii and just realized that his Hotel doesn't have internet connection nor WI-FI.

UMTS usb sticks are popular these days. I take it with me on holidays.
Broadband wireless connections almost anywhere.

Do you know where he could get it in the US?

The phone companies provide the hardware and service. Usually with a 2 year contract.

Sprint
Verizon
TMobile
ATT

All have 'em.