Wireshark and OpenBTS configuration

Hi. I am using a Range Networks Dev. Kit (pretty similar to USRP from Ettus Research) which is running OpenBTS suite (OpenBTS itself, Sipauthserve, Smqueue, etc), and I need to configure Wireshark for packet sniffing tests. More precisely I need to view MOSMS in plain text (messages coming from provisioned cell phones, sent to the "outside world"). Please note that OpenBTS is running on Dev Kit (Ubuntu), I'm using Putty from my PC in order to control OpenBTS via Ethernet port (RJ45), and Wireshark is installed and running on my PC.

So, what settings I need on Wireshark (and OpenBTS?), in order to analyze/capture plain text SMS?

Thanks a lot, Doru.