"Porting" is a telephone industry term that refers to moving a telephone number from one telephone carrier to another.
All you would be doing in your case, is to set up the OBi 202 with your existing Google Voice account's credentials on one of its four service provider (SP) slots, and hook that up to your telephones, and then obtain a second Google Voice number, set it up on a different OBi SP slot, and plug your fax machine into the other telephone jack.
GV account #1 --> SP1 --> Phone 1 jack --> Telephone(s)
GV account #2 --> SP2 --> Phone 2 jack --> Fax machine
You can just delete the old 110 from the OBiTALK portal page, and it will factory-reset the device. You can then unplug it and keep it for a spare, or use it for some other application. You'd then add the 202 and configure SP1 and SP2 for the two different GV accounts.
Complete directions for configuring GV on OBi are here:http://www.obitalk.com/forum/index.php?topic=8560.msg56460#msg56460