If you are traveling internationally, you can take your cell phone with you and place and receive calls without changing the SIM card, just like you would do at home.
You are able to do this because most mobile carriers have international roaming plans which allow you to use the mobile networks of other countries. When you use your mobile phone abroad, the foreign carrier will handle the call.
To call a local number in the country you are visiting, you would dial it as if you were dialing from a local phone, without adding any country codes or city/area codes.
To call home (or any other country for that matter), you would need to add the country and city/area codes.
You can get the complete dialing instructions by using our calling codes search.
If someone local needs to call you, they would have to dial as if they were calling you while out of the country, including the country and city/area codes.
If someone from home needs to call you, they would call you the same way that they would call if you were at home. There is no need for them to add additional codes to the number.
There are a few things you'll need to keep in mind when using international roaming: