I was just highlighting the sad fact that a big telecoms company like Vodafone Greece cannot send a text to Telefonica UK (O2, Giffgaff) and any other company that uses there network, the system works the other way round.
Here is a link to a handy website that lets you lookup the network the mobile you want to text to in the UK is on. https://portal.aql.com/telecoms/network_lookup.php So if you are using a Greek Vodafone to text a UK O2 mobile (Telefonica UK) forget it cos it won't get there. PS. you still get charged.