It would have to sell at an average of 300-350k per week at least.
Before the holiday boost and after the price cut, sales were staying fairly constant at 250k.
I expect that as the holiday boost winds down, PS3 will level off at 200-250k. The exclusives will give a temporary boost in sales that might push the average up to ~300k.
Altogether, I think it will get very close to 40m. Perhaps 38-39m.