Wi-Fi service has become indispensable in Croatia, and you will have to be on an island pretty far out or way in the hinterlands of Lika or Slavonia not to find some signal. Most of the bigger cities (Zagreb, Rijeka, Split, Dubrovnik) offer free Wi-Fi in the busiest city zones, and most coffee shops, restaurants, and hotels will offer complimentary reception to their guests and patrons.
It’s getting less and less easy to make plans without access to a smartphone; even the most local of apartment owners might ask you to WhatsApp them when you arrive into town. Roaming costs can be enormous if you use your phone from home; the good news is that roaming fees have recently been abolished throughout the EU, so if you have a SIM card from another European country you can use it in Croatia too. If you don’t have a European SIM, you can either buy an international SIM card before leaving home, or bring an unlocked mobile phone with you (ask your provider to unlock it for you) and pick up a cheap local SIM card in Croatia. You'll then have a local number and can make local calls at local rates, as well as having some data allowance. The largest local networks in Croatia are VIPnet, Tele2, and T-Mobile; just pop into one of their shops to pick up a SIM. If you run out of credit, you can top up at any local newsstand.
Calling Within Croatia
To make a local call in Croatia, dial the area code (if you are not already in that area) followed by the number you wish to reach.
Area and country codes are as follows: Croatia (385), Dubrovnik (20), Split (21), Zagreb (1), Rijeka (51), Pula and Istria (52), Osijek (31).
Calling Outside Croatia
To make an international call out of Croatia, dial "00," then the appropriate country code (Australia 61; Canada 1; United States 1; and United Kingdom 44).