Does anybody have experience with running a VoIP (e. g. Asterisk) on AWS?
But even with smaller instances, AWS network performance is going to be about the same as any VPS provider. The only way to get guaranteed performance is to do Colo, which is expensive.
At first, I used instances that were not very performant, causing some problems. I quickly moved to more powerful instances and since then there have been no problems at all. There is a slight delay, which is normal, since the servers are not in the same country as the users anymore, but the users haven't noticed it at all.
I can't say how well it scales, though. I have a small user-base, so scaling has not been a problem yet. Network performance might become a problem if you have a huge user-base.