Unless your existing taxi services were wildly over regulated, wildly profitable, or paid very well, that price reduction might be temporary. The cars must still be paid for and maintained and fueled. The drivers still need to pay for food and shelter. There is only so much room to move on costs.
It could well be that a globally managed booking system is enough to kick the tires out from under traditional taxis, but I think the other costs have a much greater role in final pricing than mere booking.
The key is to figure out why Belgium's taxis are so expensive in comparison to other places.
What are the differences in regulation?
Are Belgian taxi drivers each completely independent operators responsible for covering all their costs with only one driver while other places have vehicles shared by multiple drivers?
What are the differences in standards of living and employment opportunities? In my experience, people migrate away from low paying jobs quite quickly when the opportunity arises. For example, in Canada you won't find anyone other than management deliberately making a career out of working in fast food because the pay and working conditions are crap. The only reason anyone works fast food is because of lack of better options. That's what's killing fast food in certain places in Canada. There have been so many well paying jobs in the oil sector for long enough that in places like Fort McMurray, McDonald's and Tim Hortons have often had trouble staffing their outlets.