There are no bolt ons for any of those places.
Turn off voicemail, put your phone into Aeroplane mode and just activate Wi-Fi and use that.
Check if there are international SIM cards that allow cheaper roaming in those countries.
Using O2 will be horrendously expensive
Making calls £2/min
Receiving calls £2/min
Sending texts 50p/text
Using data £7.20/MB
This is not O2 and we are all customers here similar to yourself and cannot answer account type queries.
