Hi Richard ,
Some of our modems are network-locked, so firstly I'd recommend contacting customer services on 191 and having them check the IMEI number to make sure you don't need it to be unlocked first
After that, the modem should work fine on a Vodafone Greece SIM card, but you'll need to change the APN settings again to match those that Vodafone Greece use. You'll need to contact them directly to find out what those settings are.
I trust this helps
Jon
eForum Team