There wasn't a need to pick up the calls as I find the location pretty accurate and had not face any issues not locating the drivers and vice versa. Pretty sure there is roaming charges for the calls with non CN numbers.
And yes, switched to CN number too to resolve this issue to be contactable by drivers.
The two incidence that drivers trying to call me:
1. I went to a scenic place in the morning. Then afternoon booked a didi to go back to hotel. The booking was accepted. But then somehow due to large crowd, the part of the road leading to the park got 封路。So the driver tried calling numerous times that I refused to pick up. At the end, he cancelled the booking (and I have to walk about 2 km out of the park to the main road to book another didi).
2. Booked a didi to the airport. Address no issue as it was a 'saved' location in my app. Somehow the driver parked opposite my hotel building and so he couldn't find me (he is the only one who parked opposite among my about 10 bookings for pick up at same hotel location). He tried calling and calling and I was a bit panicky coz almost late for airport. At the end, he texted me and found me eventually (wasted 15 min).
*Should have used my China Alipay to make the booking instead to save the troubles (used Spore number Alipay by mistake).