I added AT&T international day plan to my account before my trip to Hong Kong. After arriving at HK yesterday., I am connected to local CSL network. I have data access which is great. But I can't make or receive calls to/from local Hk number or US number. I got error message saying the call can't be completed, error code Message 6, US01LV. Chatted with at&t customer service for 2 hours and they couldn't figure out this one.

For those who had used the plan in HK, are there steps I need to do to make calls, or adjustments to my phone settings? I am using iPhone 6 Plus.

Thanks.