I looked all through the forum and could not find an answer to this one.
Is it possible to use the USB port to connect a 3G modem to the Obihai 202?
If not, what would be required to do this/
You didn't find an answer because it's not possible. The USB port can only be used for the OBi WiFi or Bluetooth adapters.
In theory, you could use an ObiWiFi adapter in the OBi, and then associate it with a WiFi/3G hotspot modem, but my guess is that the signal quality issues will make for a crappy telephone experience.
You can connect the OBi to a computer with a WiFi connection.
I don't have a 3G dongle, but I assume you can do the same with it.
Windows 7
Control Panel -> Network and Sharing Center -> Change Adapter Settings
Right click on the Adapter that has a connection to the internet.
Click Properties.
Click Sharing Tab.
Check "Allow users to connect...."
Ok
Connect the OBi to the ethernet port on the computer.
There are some routers that'll accept a 3G modem as well.
IMO, 3G modem dongles (USB plug) are obsolete. The more flexible option is a 3G/4G hotspot (or, trademarked, MiFi), or a smartphone with WiFi tethering service. Wireless WAN on one side, Wireless LAN on the other side. Works with tablets, laptops, OBis, whatever, as long as the client has WiFi that can connect to the hotspot.