Very true. What OP should really do is keep their phone in airplane mode and turn on WiFi. OP should be able to utilize wifi calling/texting to US numbers without any additional charges.

It's what I like about the DIGITS app. I can insert a foreign SIM in my phone and still have my US number available to call/text when needed.

Edited to add: it should also be a regulation that US cell phone companies allow phones to be temporarily unlocked when traveling abroad. I can't believe T-Mobile is the only one that allows that.