I have built an application that fetches data from an SQL database and plots the data on a map as a marker. In order to upload the data, I am using a NodeMCU attached to a GPS module.
Currently, I am walking around using the wireless hotspot on my phone that the nodemcu connects to. However, with the current set up it means that a WiFi point is always needed.
I want to connect the NodeMCU to a 3G network, so that it can upload to the database via the 3G network as opposed to my Phones hotspot.
Most WiFi devices, including your NodeMCU, do not also have the components required to connect directly to a 3G network.
Consequently you have to use an intermediate device such as the hotspot on your phone or a router in order to connect such a WiFi device to a 3G network.
I was able to connect my NodeMCU to my iPhone using my personal hotspot over 3G/4G. If you follow my tutorial on the NodeMCU server, you can connect to a 3G/4G device with hotspot capabilities: