Re: It's only a challenge...
I have run VOIP-only networks going as far back as the late 90-es. If done properly the quality and reliability is significantly higher than PSTN at a fraction of the cost of PSTN.
Anyone having issues with VOIP either does not know what they are doing or is trying to cling onto the remnants of PSTN resulting in a "have your cake and eat it" situation. Mental experiment: "Have cake, eat cake, there is no cake". You either go all the way and do it properly or not do it at all.