Originally Posted by
BigFlyer
They don't have to look for a top level domain country code. There are vendors that have databases which will provide the location of a specified IP address.
I believe that all of the scenarios in your post are correct.
I was thinking either the TLD or looking up the IP block. However, I think looking up the IP block is too complicated. I'm curious to see if it's the scenario of connecting to a non-T-Mobile network first. An easy check without incurring charges would be to subscribe to a US based VPN service and do a WiFi call back to the US.
I think the reason T-Mobile did this was to offer the 20 cents/min calling if in a Simple Choice location to those without stateside international plans. That way, people can use the 20 cents/min calling over WiFi too. Before Simple Choice, there was never a distinction between US and international WiFi calling. With the change, T-Mobile broke free international calling for those with international calling plans.