Installing minimal command line system with netinst.iso

[Richard Owlett <rowlett@cloud85.net>]

I have limited internet connectivity.
I have read over the years that installing a *MINIMAL* command line 
system from netinst.iso [without internet is possible].
The intent to add pieces later assumed.
Is this process described somewhere?

I've got a system that appears to have a very minimal shell running.
My potential internet connection is a USB connected hotspot from 
T-Mobile. On a typical GUI installed Debian it runs fine.

My minimal system doesn't recognize it.
What might be the missing software?

Any suggestions?
My effective data cap at the moment is ~1 GB/month.
Among my goals is installer for those with _*minimal*_ resources.

TIA