Pase internacional

My mom is going to France. Will be getting her the $50 for 30 days International Pass. She has the ONE plan.

1. I am very confused about their unlimited calling with the International Pass. Is it unlimited for normal cellular signal calling and $0.25/minute for wi-fi calling?

2. If my mom calls Indonesia from France, is it part of the unlimited calling? Same thing, if someone calls her from Indonesia while she is in France?

3. I am assuming calls to and from the US to France is part of the unlimited calling?

4. Should my mom keep her wifi-calling turned off during her trip?

5. Should my mom keep her roaming turned off during her trip?

6. If my mom runs out of data before the 30 days, how do I add more?

7. Any other tips for avoiding surprise charges?