Currently, if you phone 999 from a mobile phone it will use any available network to make the call. Even if your network has no service the call will get through via whatever is available. That clearly will cease if the mobile networks are expected to charge for the calls.
Recently, I was at the scene of an accident where one of the vehicles had come to rest in a position that seriously endangered oncoming vehicles. I tried to call the local Police just to park something with blue lights there as a warning. What a palava. Local station number redirects to some call centre with zero local knowledge. If "you'd like a crime number to give to your insurance company, press 1. If you'd like us to actually do something press 2..."
I doubt anything worthwhile came of it, as I had such difficulty even getting the location of the incident across. Had one person with local knowledge been available to take the call in the local nick, they could have got a car there within minutes, I'm sure. I was only half a mile from the Police station.

I'm sure call centres are a nice cheap way of manning phone lines for some businesses. The business of potentially saving lives needs a bit more nouse and, as said, local knowledge at the end of the line, IMHO.