Rule of thumb, never roam!
Rates could be cheap with your local telecom provider, but there may be hidden costs, so just don’t activate your normal sim unless it’s an emergency.
Get a local sim card.See: http://wiki.apnchanger.org for info on local operators and their offerings.
Or use Skype at an internet cafe, on your phone or pc via wifi for free or cheap calls
Also, don’t take your latest / fanciest device abroad. Take an old phone or cheap laptop that you wouldn’t really mind getting lost, stolen or damaged.