[PBX vs VoIP]

Yes exactly mattlandis, PBX and voip are almost the same but different in purpose. Most of the companies typically used PBX. I am also using voip phone because it has a great quality.

[What affects the VOIP phone quality?]

I deeply agree with you Thomas that the top 1 factor that affects voip quality is the internet connection. Secondly is the hardware of course. Low quality of hardware and definitely affects the quality of voip. Lastly, the weather conditions.