This summer I will be traveling to the UK (except Northern Ireland) and Ireland.I live in America so I have a American Nexus 6P. To be able to take my phone there I need to know a few things: 1. What is a carrier that I could use in all of the countries (I am on Verizon now if that changes anything)? 2. Recommend a power converter or plug adapter that is compatible with all of the countries. 3. Recommend a power bank to use. Thanks!