Iphone & MicroCell Booster

@setabt - first of all, the MicroCell is not a cellular booster. It is a femtocell (mini cell tower). It broadcasts a 3G signal that your phone connects to and then uses your internet connection to connect to the AT&T Mobility Servers. A cellular booster receives a weak cellular signal and then "boosts" it to useable signal.

In most cases a MicroCell would work provided you have a post paid AT&T cellular account and a good internet connection. However, the MicroCell has been discontinued as of the end of 2017.  AT&T is not selling them anymore so the only place to find one is eBay or someplace like that. There are caveats to purchasing a used MicroCell which are covered in my Tech Guide (link in my sig line). AT&T says they will continue to support the MicroCell thru this year but I have my doubts as to how reliable that will be.

What we are recommending now, and what AT&T will try to sell you on, is WiFi-C (WiFi Calling). WiFi-C actually works better than the MicroCell but you still need a post paid AT&T cellular account and a phone that is WiFi-C capable. There is no cost to WiFi-C other than the phone. Your iPhone 8 is WiFi-C capable but the 5S is not. SE and above are the only iPhones capable of WiFi-C. So, your options are to upgrade the 5S to at least the SE, purchase a cellular booster (which are pricey but do work well if you have at least one to two bars of signal strength), or switch carriers to one that offers better cellular coverage.