Not to put too fine point on it al3x1k0, but not everyone has contract phones with roaming to begin with. I use a 'smartphone' as an actual phone only. I know that may be a startling statement to some people but it's true. I use a prepaid phone only and it costs me $100 CAD per year. That's it, $100 per year, not per month.
So if I wanted to have a cellphone when travelling (which I never do), then buying a local pre-paid sim card would make sense to me. When I am in Greece, I actually just buy a 'pre-paid phone card' which I then use in the local public telephones to make any call I need to make. I've used cards on many trips to Greece with no problem making local or international calls.
Here is a good description of the options gaume.
PRE-PAID CALLING CARDS-Pre Paid Calling Cards