Based on my experience with Asterisk this should be as close to a set and forget service as I can think of. Meaning I literally will not even reach out to support on any normal year. For that, $400/mo should be plenty of margin. But I might be missing some unknown technical hurdle I have never bumped into.
In order for a company to get $100k/mo of revenue it needs to get 250 customers each at $400/mo. Each of these customers is likely to compare it against running their own Asterisk in a cloud for $100/mo and headaches. It is a horrible pool of clients to have because members of this pool think $1.5k/mo for what supposedly is a critical service for a company ( voice + text ) to interact with its "old school" clients is too much money and every two days they are looking at integrating with voip.ms so they can build dropbox using FTP.
