I don’t believe there are any examples showing basic serial port operations on mangOH just yet, though there are plans to provide this as part of the tutorial series in the near future - see this post.
Regarding serial data, I can recommend these two pages which I found to be a good reference for information on Linux serial port programming:
Ensure your Legato application has permission to Read and Write to the serial port(s). Add the following to your application’s .adef file and modify to suit your needs.
// Get read and write access to the USB Host port.
// I.E. for use with a FTDI USB Serial Device
[rw] /dev/ttyUSB1 /dev/ttyUSB1
// Get read and write access to the UART1 port.
[rw] /dev/ttyHS0 /dev/ttyHS0
For example, If I had a USB serial device plugged into the USB Host port on mangOH, the application needs permission to read and write to /dev/ttyUSB1. Remove the device(s) you don’t need.
I think Raf did a good job of providing some information about serial communication. Can you provide some more detail on what magnitude of data you expect to be sending over the 3G network and whether there is an existing network protocol that you intend to use? With that information, I might be able to give some suggestions.