One really handy feature on cell phones is that you can prefix the country code with + and the phone will dial the number for you correctly for local calls and long distance. i.e. to call me you would start with +1604… 1 being the country code for Canada.
One of my friends was updating his new number on my cell phone a while ago, he missed entering the country code, resulting in the area code of 250 being the country code. What county is 250? Rwanda. So I must have woken up some poor guy in Rwanda trying to get a hold of my friend later that day. Luckily Fido has per second billing so it didn't cost me too much.
Moral of the story, double check phone numbers that someone else updates in your phone.