As far as I know, the racing missions aren't unlocked until Verdant Meadows becomes available for purchase.
Unlocking the races also unlocks the *airplane* races, and they don't want the player to be flying around in airplanes before they've been officially introduced in the story line. So the call comes pretty soon after the airstrip becomes available for purchase.
I could be wrong, but I don't think Deconstruction has anything to do with the call that unlocks the races. That's still too early in the story line. (Other than obviously that it needs to be completed to go on in the game.)
There IS a call where (*MAYBE SPOILERS*) Wang Autos is unlocked for purchase. That comes pretty soon.
After Deconstruction you get a call saying that you can go to the driving school, not the races.
All the game races are unlocked sometime around Las Venturas, maybe around/after the flight ones. You may have to complete flight school first becuse there is a race selector thing inside the airport of Venturas. It contains races (that aren't really races) where all you do is fly around in a plane.