Free Wireless Access
The easiest way to get online is via WiFi. The vast majority of hotels and private accommodation offer free WiFi and there are connections at nearly every cafe and bar plus some restaurants. It's not always advertised but it's there. Just ask your server for the password. Currently, Rijeka is the only town to offer free wireless access from its main street, Korzo. Airport, rail stations and bus stations in major cities offer free wifi which is highly convenient if you haven't yet set up your data connection.
Croatia's major cellphone carriers--Tele2, VipNet, T-Mobile--offer the possibility of buying a data package along with your SIM card. See more on cellphones in Croatia.