Mirissa is in Sri Lanka's telephone area code 041, which is +94 41 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 Nawalapitiya, Sri Lanka is 94, (0)54.
The country code and area code of Matara, Sri Lanka is 94, (0)41.
The country code and area code of Mannar, Sri Lanka is 94, (0)23.
The country code and area code of Anuradhapura, Sri Lanka is 94, (0)25.
The country code and area code of Kurunegala, Sri Lanka is 94, (0)37.
The country code and area code of Ampara, Sri Lanka is 94, (0)63.
The country code and area code of Awissawella, Sri Lanka is 94, (0)36.
The country code and area code of Batticaloa, Sri Lanka is 94, (0)65.
The country code and area code of Chilaw, Sri Lanka is 94, (0)32.
The country code and area code of Galle, Sri Lanka is 94, (0)91.
The country code and area code of Hambantota, Sri Lanka is 94, (0)47.
The country code and area code of Hatton, Sri Lanka is 94, (0)51.