North American area code +1 315 is for Syracuseand Utica, NY, USA, and surrounding areas of north central New York other countries have a "315" area code code +31 is the Netherlands, and numbers beginning with +31 5 are in the northeast part of the country.The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America USA, Canada, etc. uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.