Just to follow up on FGD135's query, 330 knots IAS at sea level is about mach 0.6 (going from memory here). 330 knots at FL 280 is about mach .81. 330 knots at FL 350 is going to be mach 1. something. So as NZScion points out, we climb at the desired IAS until it turns into/ translates to/ becomes the mach number that we intend climbing at.
At that point, as we climb at that constant mach number, our IAS will decrease. IE .79 at FL 300 is about 330 knots IAS. .79 at FL390 is about 240 knots IAS. (OAT plays a part in all of this as well but you get the general idea).