I have something similar setup, but it is with async voice so not waiting on the line for it. Can also send my idea without network connection, so not waiting on phone to ring/ pickup and connect.
By async voice, do you mean you record a voice memo and have that processed into a brief? That definitely sounds like a low-friction mode for quick, offline capture.
The live on-call model is interesting to me because it enables a back-and-forth conversation. The agent asks clarifications, suggests alternate approaches, etc. Something about being able to talk ideas back-and-forth helps me refine my idea more.
But async voice memos feel like a really useful complementary mode...