Back to the question of asking Acft to "report heading/speed".
As said above, using the phone each and every time to announce the heading (or speed) to the next sector would be a huge workload (in approach), and is not justified (most of the time).
Another factor is that it takes time to place the phone call. I mean, if you place that call, you have to wait for the OK of the next ATCO before you can "shoot" the acft on the next frequency. The delay is not very long for 1 acft (let's say 30sec), but if you do it every time...
