Using an expired SIM card in Airplane Mode I have iPhone 6S. My mobile phone and data plans are with Ting, a US-based mobile virtual network operator that uses the framework of the US-based Sprint Corporation telecommunications company. I'm currently not in the US. I've turned on Airplane Mode, and then switched on Wi-Fi. The caption "Sprint Wi-Fi" appears on the top left of the screen, and I am able to access the Internet over Wi-Fi.


How does my phone know to show the word "Sprint" in the caption? Does it read it off the SIM card, or does it get this information over Wi-Fi, or some combination of both?
If I discontinue my Ting/Sprint membership, and stop paying my monthly subscription fee, but keep the SIM card inside my phone, without ever turning off Airplane Mode, will the caption still read "Sprint Wi-Fi"? Will my phone continue to behave as before?
Are the answers to the questions above specific to Ting/Sprint, or will they remain true regardless of the mobile company I'm a member of (with the difference that, instead of "Sprint Wi-Fi", the caption "XXX Wi-Fi" will appear, where XXX is the actual mobile company)?
The reason it says "Sprint Wi-Fi" at the top of the display is that you currently have "Wi-Fi Calling" enabled. This means that your calls and text messages are sent via Wi-Fi over the public internet to Sprint instead of being transferred via a cell signal. This is a helpful feature when you haven't got a cell signal, but have an internet connection over Wi-Fi.


The word "Sprint" comes from the packet gateway that the phone connects to over Wi-Fi. It is not read off the SIM-card as such. Your provider Ting has a cooperation with Sprint to use the packet gateways of Sprint to enable this feature.
If you cancel your subscription with your provider, Wi-Fi Calling will also stop working. It doesn't matter if you're in AirPlane mode or not - when you try to place a call using Wi-Fi Calling it will be rejected by Ting/Sprint if you have cancelled your subscription. 
These answers are not specific to Ting/Sprint, but are true for any cell provider that supports Wi-Fi Calling.