I don't know what the system is in Europe- but can one buy a SIM card for my phone in Barcelona? I'll need it to work in the ports during our Med cruise- Italy and South of France. Turkey would be a bonus! Roaming charges from India are prohibitive so this will be cheaper if I can find a single SIM. We'll have time in Barcelona to get one. Any suggestion?

T-Mobile is the largest European carrier - you should be able to find a store that will sell you the SIM. You might also consider using Orange - they are also quite large. Be sure your mobile phone is "unlocked" so that it accepts the new SIM.