will i be charged for this? how much?

sorry if this is a weird question. my friend who is currently in guam accidentally called me, and i picked up on reflex. as far as i know i don’t have international calling (on my parent’s plan so i’m not sure what plan), and i can’t find any information on how much it would cost, or if it’s even considered international as guam is a U.S territory. the call was 25 seconds long.