I'm currently in the US and have roaming enabled on my mobile. Yesterday and today I've been receiving calls from "NZ mobile" numbers that are obviously spoofed. Thus far I've seen the following CLIs:
+64 27 755 900
+64 25 550 241
+64 28 096 158
+64 25 214 573
They're obviously fake as Telecom/Spark never issued 6 digit 027 numbers. 025 was taken off Telecom and put into protected status when the TDMA network was shutdown a decade ago, and the 028 number is way too short as that is managed as an 02xy network prefix range.
I'm guessing that if you actually answer the call you'll get connected to some premium rate service that bilks you...
I've since put my mobile in airplane mode with wifi on.