U.K. travel

Well, if you’re on a postpaid plan from the last few years, you should be good. Phone calls are 25¢/min, texts are free and data is free but slow (currently ~256 kbps). The best way to communicate while abroad is via a VoIP app (e.g. Skype, FaceTime, Viber, GoogleVoice, etc), since you won’t be charged. I’d suggest that everyone in the group decide on an app and use it to communicate between members of the group. Also:

1. I’m told that you are no longer charged for calls you let roll over to voicemail. I don’t know about calls you reject, so beware.
2. Use Visual Voicemail to listen to your messages. Don’t call the voicemail system.
3. Calls to the USA made on WiFI are free but overseas calls made while on WiFi can be expensive, as they are charged at your international rate. Any calls to the US and “normal” countries (i.e. not North Korea) are 25¢/min while roaming on cellular.
4. To make sure that you are either on WiFi only or cellular only either turn off WiFi or put the phone in Airplane mode and turn WiFi back on. Left to their own devices, phones have a way of picking the most expensive mode of calling.
5. Figure out how to preload Google Maps offline data while on WiFi, to save on your data usage.

In UK you’re probably going to be roaming “EE”, which is a T-Mobile company. This should give you a certain amount of high-speed data.

https://www.t-mobile.com/support/coverage/international-roaming-checklist