Good day!
I develop a website using Ruby-on-Rails and Jquery. This site has a feature to play files from an IVR system right in browser window, without downloading it.
Since GSM is not supported on any browser ( see this table) you will need to convert it before.
Now you have two options, you can convert on-the-fly or convert any files you already have and will converting the new ones as they are created.
You can use ffmpeg to do the job, with streamio-ffmpeg gem or you can also find a SaaS solution for the job.