Is it not postpaid?
I used VIP for data, primarily because I had a VIP voice SIM with quite some credit on it. I made only one phone call (another Croatia mobile network), and that one call was truly expensive. I am not used to such high domestic rates in Hungary.
I normally used my phone's built-in SIP VoIP client either through WLAN or 3G, and I was quite satisfied. Sometimes a bit of a delay, but I was compensated for by the price that these calls cost
I also bought two T-Mobile HR starter packs for 1 kn / piece. They are not activated yet, but when I saw that during the 2 minutes we spent at a Pula newsagent, about 4 people bought 1, 2 or even 6 pieces of these packs, I decided to buy two to find out what the pack is good for

As far as I understand, it comes with 10 kn credit, and if I top it up with at least 50kn, I get another 50kn, plus 1000 minutes network-internal calls. But I am not sure.