First thank you all for your answer. I'm so glad you want to help me. This topic can help more non-Croatian citizens.
I'm going to send these my question to Croatian providers and I wonder what they will offer me.

Now a little bit off topic (no mobile internet topic) but it can help to choose provider:
I haven't found the price of sms and mms abroad (I've found only the price of international call). Does the sms (or mms) abroad cost the same price like to Croatia?
If yes than it is very interesting for me (it is much cheaper than sms roaming). International call costs approximately the same price like roaming call. In this case is TELE2's price 0,99 Kn per mms it very attractive (tariff PLAN NULA) but if you say TELE2 doesn't have good signal coverage on the sea, it is not acceptable provider for me and I respect your recommendation.

Thank you