How Do I connect to a serial port on a WR21 from a remote location?

I have a WR21 with a ATT cellular plan. The TransPort will never be on a network at the remote location. I need to read/write to the serial port, only using the cellular plan to control a CP1H OMRON PLC

I am new to this tech and have scoured the documentation.
any help in pointing me in the right direction would be great.


There are several app notes on the site, this one deals with serial port, hope it helps.