Is use of familiar contacts seamless while abroad?

[Latitude42]

My daughter starts 15 days of travel in Republic of  Ireland and UK (specifically, Northern Ireland and England) with an iPhone 5S. The VZW travel tool says the phone is good to go using VZW TravelPass. Neither of have ever used cellular communications outside the US and Canada.

Will she be able to phone and text me and others in the US just by picking from her contact list? Or will she instead need to compose +1 (heavy zero, one) plus the US phone number on the front of everything?

Similar questions:

1. In the event that I or somebody else n the US phones, she doesn't pick up, but notices the recent call later, will the recent call be remembered with the +1 prefix, ready to go for instant callback?

2. If she receives an incoming text from me or a US friend, and she replies to it conversationally, will that work seamlessly?