Five head-to-head comparisons, each written to concede the cases where the other platform wins. Bland is cheaper per minute at scale. Vapi has a better builder. Synthflow is faster to self-serve. Retell has cleaner developer ergonomics. If one of those is your binding constraint, buy theirs.
Every one of those platforms sells infrastructure or a builder. We sell a finished, integrated, evaluated agent and the weekly work of keeping it good. If you have engineers and want to own the build, a platform is the right answer and cheaper. If you do not, a platform is a project you will not finish.
Advertised per-minute rates almost always exclude the reasoning layer, the integration work, and the tuning time. A $0.09 platform minute becomes considerably more once you add the model call and amortise the engineering. That is not a criticism of those vendors — it is a comparison error buyers make constantly.