That's one of the sticky points with having a GSM phone when traveling abroad (outside of US/Canada). You'll be roaming internationally, and a call may get forwarded to your voicemail if you don't answer.
However, most likely you'll be charged twice: once from the home switch to the "visitor's" switch, and another from the visitor's switch back to the home switch to route to your vmail.
The lowest-cost solution would be to keep your phone off after you take off for your int'l flight, so your phone is not recognized as roaming. Then, upon arrival, buy a local SIM card to make your calls, and give your contacts your local temporary number. The advantage is many foreign networks do not charge for incoming calls; the obvious but minor inconvenience is having to deal with an extra phone number.