Here’s my latest piece for the local paper (West Sussex County Times) that came out yesterday.
If you are dogged by poor mobile reception, but have access to WiFi, then your prayers have been answered.
http://www.wscountytimes.co.uk/news/columnists/try-making-a-phone-calls-via-the-internet-1-5730669
You can link a Vonage account to an App on your Phone. Not sure if that helps.
Otherwise I think most of the Apps only work in the US