Who I have the same questioned this topic

We will be traveling in Europe for about 2 1/2 weeks.  Spain, France, Italy, England, Malta, and Greece.  I have a few questions, as I've never taken a cell phone out of the country yet...

1. Receiving Calls, texts.  Do I get charged if someone calls me and I don't answer and they leave a message?  Do I get charged if they text me?

2. If I send a text, do I get charged per text? (I saw a $10 a day data plan, but not sure not the specifics of this, I don't understand MMS, etc.)

3. If I only use wi-fi to post things/pictures on social media, is there any charge on my phone?

Basically, I want to know what I will get charged for if I turn my phone [iPhone 6s] on in another county.  I don't want to answer or make any calls really to anyone while on vacation, but would like my kids to be able to get a hold of me in an emergency, but what will the charges be for a text back and forth?  And, if I try to only use wi-fi to post on social media, will there be charges from Verizon? (I know that not all wi-fi is free, so I would get charged somehow if it's not...would this show up on a Verizon bill?)

Thanks for any help!