Both International Day Pass and Travel Pay Per Use are on my Device, which takes precedence?

The international day pass takes precedence. The pay per use feature is needed for you to roam plus it covers you in any non day pass country.

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And if your plan allows roaming for free, like in Mexico and Canada on some of the newer plans, neither of those will be charged. 

OK, so I shouldn't delete the travel pay per use, otherwise it will impair my IDP use?  Also I think I have the following right, can you confirm?

.  On days when not doing any calling/texting/data use, turn off Data roaming to (for certain) not get IDP charge

.  Incoming calls/texts trigger IDP usage.

.  Google maps app (or other apps on phone which use data) triggers IDP.

.  New feature that I hadn't noticed 5 years ago with IDP.  The maximum you can be charged on a line is 10 daily uses of IDP in a billing cycle...so about $100/line. 

@formerlyknownas

Yes, one of the options I was considering (have a short trip to Canada) planned was to look into adding roaming for North America .  Do you happen to know if it is an option that you can add to an existing plan and then take off?  I like my plan as is, and don't want to change it, it might even be a grandfathered plan.  I don't foresee going to Canada often, so the IDP may work just fine for me.

OK, so I shouldn't delete the travel pay per use, otherwise it will impair my IDP use? 

Correct, do not remove the pay per use feature. Removing it could prevent roaming at all.

Also I think I have the following right, can you confirm?

.  On days when not doing any calling/texting/data use, turn off Data roaming to (for certain) not get IDP charge

Correct.

.  Incoming calls/texts trigger IDP usage.

incoming calls, yes. Incoming texts are free and do not trigger IDP. Sent texts will trigger the IDP charge.

.  Google maps app (or other apps on phone which use data) triggers IDP.

Correct, any data use triggers IDP which is why you should leave data roaming off unless you want to use data because your phone will use data even if you aren’t actively using data, if you let it.

.  New feature that I hadn't noticed 5 years ago with IDP.  The maximum you can be charged on a line is 10 daily uses of IDP in a billing cycle...so about $100/line. 

Correct.

@sandy708

Yes, one of the options I was considering (have a short trip to Canada) planned was to look into adding roaming for North America .  Do you happen to know if it is an option that you can add to an existing plan and then take off?

That entirely depends on if you have a plan that allows roaming North America feature. Some of the older Mobile Share value and Advantage Plans did. But only if you had a large data pool and a good number of lines

  I like my plan as is, and don't want to change it, it might even be a grandfathered plan.  I don't foresee going to Canada often, so the IDP may work just fine for me.

If the roam North America feature is not available to you, then you won't have any choice but to use international day pass.

Please make sure you add international day pass before you leave the country.

You can control whether or not you are charged the daily fee by turning off data roaming, don't answer your phone, and don't send text messages. 

https://www.att.com/international/day-pass/

OK, so I shouldn't delete the travel pay per use, otherwise it will impair my IDP use?  Also I think I have the following right, can you confirm?

The $0 travel pay per use is a permission for the phone line to Rome. Without the $0 travel pay per use enabled roaming is blocked. Many report that with International day pass turned on this feature disappears from their plan add ons.

On days when not doing any calling/texting/data use, turn off Data roaming to (for certain) not get IDP charge

You can turn off data roaming all the time if you want. Data roaming will run in the background and will incur the $10 per day charge. If you are trying to avoid the charge leave data Roaming In the off position, do not make or accept phone calls or send a text messages and you will not be charged. 

.  Incoming calls/texts trigger IDP usage.

Partly correct...

Incoming text messages do not trigger International day pass charges.

Incoming calls that you accept will encourages

Google maps app (or other apps on phone which use data) triggers IDP.

You are describing data usage. Any service or application that uses data, and if you leave data roaming on with data Roaming In the background, you will incur the $10 per day charge. 

New feature that I hadn't noticed 5 years ago with IDP.  The maximum you can be charged on a line is 10 daily uses of IDP in a billing cycle...so about $100/line. 

Slightly inaccurate. You are charged for 10-day pass uses per bill cycle. If your trip extends over two Bill Cycles or more, you can be charged $100 for each bill cycle.  A second phone line using service on the same day will only be charged $5.

So for example if you and a second person on the account, travel to Canada for 15 days, and both use all 15 days worth of service, your charge is $150.

I would encourage you to use the link that I posted above to the international day pass which includes some frequently asked questions. A lot of what you have asked here is already answered. There may be other things which you have not yet asked and should know and is included on that information page.