With regard to mobile/ cell phone usage this is reasonably covered. The article below details HM Gov's approach in both a Deal and No Deal scenario. The price cap would actually come down £5 / E5 to £45 with the current EU set limit being £50. I have repeatedly pushed my own cell phone provider ( Three) on this subject. They have generally been well ahead of the curve providing "feel at home" services on a global scale rather than just within the EU and have said they are working towards & operating on the basis of an 'as is' continuation of the service as they had negotiated on a country by country basis ahead of the legislation in the most part when it comes to the EU. I have had to accept that the level of detail they can provide is limited as they are commercially sensitive. Obviously I can only speak for their position but in our discussions ( over several months now) they see it as a commercially positive move and a good sales tool IF EU 27 providers dont want to play ball as their own pre existing agreements mean they are mostly unaffected. I've tried to keep this focussed on knowledge provided keeping my own feelings on how I think they will act & again I have no idea how it may affect other providers.
https://www.gov.uk/government/public...no-brexit-deal