Hi, How are you?
Upon reading brief details I believe its a doable job I have great experience doing projects with UNIX. I am confident about getting this done. While I believe we need to have detailed discussion aboutFlere
Sir, how about I use a 4G /2G SIM card + one tiny linux MCU (or rasperberry pi) ,the total hardware cost will <20 USD or 50 USD (dependng on hardware ) ,and I will help you implement answer machine functions on that hFlere