SMS gateway with Android OTG

Hi comm,
I want to build SMS gateway and call commands from Android OTG serial.
What can I see, there is only kits in stock.
According to Partice post: Sending SMS from Particle Electron using AT Commands “Electron 2G Kit” is it possible to use it with private SIM?
I don`t want any extra stuff. What I need to achieve this?

If you search the forum for “3rd party SIM” you will find lots of hits.