I knew it. Sonera is in trouble with their ancient way to build up 3G/GPRS data packets. Finnish communication authority (Ficora) published their study (in Finnish) and mobile data grew a lot.
So, our family is moving towards elisa and fixed data prices. I've already done that with two business subscriptions from Elisa. 3G packet with 384 kbit/s speed limit is 9,95€/month. I think it's reasonable and for our business use more than enough.
I wish Nokia could keep up with the pace, since E90 struggle is something very special from their side and as demand for mobile IP is gaining, manufacturers should be able to keep up with the pace.