Killarney is in Irish area code 064, which is +353 64 in international format.
(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.)
The country code and area code of Letterkenny, Ireland is 353, (0)74.
The country code and area code of Carlow, Ireland is 353, (0)59.
The country code and area code of Ennis, Ireland is 353, (0)65.
The country code and area code of Clonmel, Ireland is 353, (0)52.
The country code and area code of Portlaoise, Ireland is 353, (0)57.
The country code and area code of Longford, Ireland is 353, (0)43.
The country code and area code of Castlebar, Ireland is 353, (0)94.
The country code and area code of Dundalk, Ireland is 353, (0)42.
The country code and area code of Drogheda, Ireland is 353, (0)41.
The country code and area code of Naas, Ireland is 353, (0)45.
The country code and area code of Athlone, Ireland is 353, (0)90.
The country code and area code of Tralee, Ireland is 353, (0)66.