Because your phone is connected to a switch that is not North American, and the farside switch (which is what you're connected to in Europe, say) is sending call progress indication back in-band to the person calling you from Canada to avoid "clipping".
Before VoIP, in ISDN Q.931, it could be done either way if it was ISDN end to end, BUT, if the local Canadian switch generates the call progress tones, when you answer and say, HELLO, he will hear LO, and the HEL will be clipped or lost because of the lag in the CONNECT message getting back to his switch out of band via SS7 saying you picked up the phone. SS7 is a packet based network but the actual voice path is time division multiplexed in a "circuit". Nortel said screw this and it was done inband on ISDN to avoid that clipping. There was no way around it.
Out of band signaling had to be implemented because hackers were using cereal whistles to redirect calls.
Cell phones work the same way.
Can the switches be programmed to identify the originator and give them the proper cadence. Yes. Did anyone want it done? No.
DMS for example, was enhanced to provide a different kind of ringing tone back to the originator if the terminating party was on a call and receiving a call waiting tone vs. if the phone was on hook and actually ringing.
So, when I would say, why didn't you answer you jerk and he would say I wasn't here, I would say ... LIAR!!
RING AGAIN NO ANSWER was even more fun. You dial and there's no answer. The next time the jerk uses his phone and finishes the call, DMS would ring you and then ring him. If he didn't answer you knew he was ignoring your call on purpose ... unless he dashed off to the bathroom.
You can't create that kind of transparency. The Rogers MF275 confuses my Nortel phones into nervous breakdowns. Now their IGNITE home phone and even the packet cable based one can never fake what it expects to see.
