International calling if no plan

Yeah you already discovered it - it's called Wi-Fi calling and texting. It allows your phone to work over a local Wi-Fi connection as if you were still in the United States.

AT&T prepaid $40 a month plan includes free usage in Mexico and Canada.  

The WiFi calling webpage as a number of FAQs that may be helpful.

https://www.att.com/features/wifi-calling/

We are here to help with your international calling concerns, @Adfriedman2.

Thank you to the ACE's for the help. 

We understand how important it is to be able to stay connected. As mentioned above, Wi-Fi calling is a great way to stay in touch. To forward calls, you must be in range of the cellular network when you set your iPhone to forward calls, or calls won't be forwarded. You can not forward calls to an international number.

We hope this information helps. Thank you for contacting AT&T Community Forums. Please feel free to reach back out with any other questions or concerns.

Clarissa, AT&T Community Specialist 

So even if I have a burner prepaid phone to use for a couple of weeks   Even if ATT with US local number and use international minutes on it  if I take it with me to Europe will not be able to forward calls from my  work iPhone number to it? 

Hello @Adfriedman2, we are here to help with your international calling concerns.

To answer your question, no you can't forward calls from your iPhone to your prepaid number while in Europe. To forward calls, you must be in range of the cellular network when you set your phone to forward calls.

Let us know if this helps!

Mellira, AT&T Community Specialist

So even if I have a burner prepaid phone to use for a couple of weeks   Even if ATT with US local number and use international minutes on it  

There is no such thing as adding "International minutes" to AT&T prepaid.   

if I take it with me to Europe will not be able to forward calls from my  work iPhone number to it?

No.  

Your first question was about Mexico which is included free on the $40 and up Prepaid Plan. Now you've transferred your question to Europe where it's not free.  And prepaid has very limited roaming for $35 per week. 

However just like in Mexico you can use Wi-Fi calling and just like in Mexico Wi-Fi calling and texting over a local Wi-Fi connection will be just as if you were still in the United States.

So will need Wi-Fi hotspot. Is there one that works best with iPhone ATT?  Tried glocal few years ago just didn’t seem to work well but was an older phone. 

WiFi has nothing to do with AT&T, unless you’re talking AT&T WiFi.  WiFi is WiFi, and your phone connects to it like any other device that can connect to WiFi.  How well it works or doesn’t work is a function of the WiFi hotspot, not your phone.