Custom Built SMS API

I'm looking for someone who has experience with building SMS API's from scratch similar to twilio, vonage ect but I'm wanting my own built so I can resell SMS and also be spam friendly as I don't want my API to be blacklisted, It'll be a big project so only text me if you know what your doing or have worked on something like this in the past.
I can pay for the maintenance of the server as you'll be hosting and also don't offer me a silly price for each SMS as it should be cheaper since there's no middle man.

Don't text me offering services like Twilio ect!