If you can't monetize it, you can at least sell the source code as an enterprise solution -- i think there are many SMB would like to get this simple system in house.
Honestly, Twilio's API is so well done I don't believe my code is worth anything. However, it's available here: https://github.com/dickeytk/callinwithus for anyone to take a look at if they're curious how it works.
Remember, people don't pay for code, they pay for solutions to their problems. The amount they are happy to pay isn't related to the code, but to their problem.
If it's easy to write the code, you will (or might...) quickly have competitors, that's all. But since you couldn't find any, that might not be the case...