Making local calls in a foreign country

How is a phone number "10 minutes away"?

Regardless, with IDP (in supported countries) you can call the country you're in. https://www.att.com/international/day-pass/

Anytime you are outside of the United States in a country not covered as domestic service that is referred to as 'roaming'.  When you are roaming you are connected to a different network other than AT&T. You may notice in the top right hand corner of your phone that it will indicate you are connected to a different network by name. 

   Any and all usage while you are roaming is covered by International day pass in countries covered by IDP. 

It doesn't matter whether you are calling or receiving a call from a US number, or a foreign number you are still roaming, so day pass will trigger a charge for that day.

The $10 international day pass charge is triggered on any day that you make or receive a phone call, send a text message, or access data services whether actively or in the background on your phone while your phone is connected to a foreign Network, not covered as part of your domestic plan. 

( your domestic coverage likely includes Mexico, canada, Puerto rico, and the US Virgin Islands as well as all 50 states) 

Let me clarify. If I were calling using my mobile while. In the US I’d preface an international call by “011” then the country code, then the phone number. The call would show on my bill as a separate per minute charge from my domestic plan.  Does the same hold true if I have IDP, roaming under a different carrier? Do I use a different calling protocol than the 011 + country code?  Is this why people buy a prepaid SIM card in the foreign country and not use IDP?

Does the same hold true if I have IDP, roaming under a different carrier?

No. Calls to local numbers are covered by IDP.

Do I use a different calling protocol than the 011 + country code?

You can dial the country code but it’s not required since you are in that country and roaming on a carrier in that country. All you need to dial a local number is the local number.

Great, thank you!

Let me clarify. If I were calling using my mobile while. In the US I’d preface an international call by “011” then the country code, then the phone number. The call would show on my bill as a separate per minute charge from my domestic plan.

As 'long distance'.  And you can purchase a $15 calling plan to reduce or eliminate per minute cost of long distance. 

 Does the same hold true if I have IDP, roaming under a different carrier? Do I use a different calling protocol than the 011 + country code?

Then it's roaming, not long distance.  IDP covers all  roaming use.  Doesn't matter who you call, any number you call. 

 Is this why people buy a prepaid SIM card in the foreign country and not use IDP?

Yes.  Roaming is still pricey.  Often local service is very inexpensive.