If you plan to stay in Malta for a while and would like to buy a SIM card you can do so in one of the following outlets.
Cost per sms - €0.05
Cost for calls - €0.24 per minute
Coin phones do exist, especially in Valletta, but are not that common. Card phones are more common than coin phones. A card can be bought in stationery shops.
The above mentioned service providers also offer internet service. For prices please refer to their websites.
Normal internet in a common household costs €23 per month.