It will depend on your carrier .... a comparison article for your reference https://www.whistleout.com/CellPhones/Guides/global-roaming-which-carrier-is-best
It aint me so I'll have to find out the carrier. I told him to call the number on his bill. Anyhow I've been task to handle it.
Call your carrier...there's a setting on most phones. I have done this several times and there's nothing to it.
If the phone is unlocked just buy a prepaid German SIM card and your good to go. That’s why we always keep one of our old phones to travel with.
Google Project Fi has the same rates for data in 170 countries, low rates for international calls, and free texts. https://www.engadget.com/2018/02/15/google-expands-project-fi-international-data-to-170-countries/
