I'm using my browser to configure the RF500S and I can't seem to find the dial in settings, where can I find it?

Dial in is no longer supported in the new firmware using the web browser configuration. If you want to use the dial in feature, you will have to go back to the software / firmware V7.26 / V4.48. To download the old software and firmware, you can go to this site:

https://webfiles.multitech.com/routers