Good point, just found the instructions. Will get out my pliers/knife to open it up and super glue to get it back closed once the replacement buttons arrive.
A case on eBay was a perfect fit for the electronic innards of my 2006 3-button Smart Key fob, for about $20. It has the red button, like the original fob; but does lack the silver logo on the case back. Search "NEW Smart Remote Key Fob Case 2+1 Button for Toyota Prius + Uncut Insert key"
I purchased one of these on Ebay from Australia, replacing the front pad was simple. Toyota Prius Repair Silicone Key Pad for 3 Button Remote | eBay
You can find them on Amazon as well, I just purchased this one (link below) last week and it came in this morning to replace the smart key case for a 2007 Prius. I added a brief overview of what you get and how to do the innards swap in the review section (also at the link below) Keyecu Replacement Shell Keyless Smart Remote Key Case Fob 2+1 Button for 2004-2009 Prius
I did want the manufacturer to add the logo but he threw all responsibility on me if customs put a stop to it. I did not like the construction of the key/back holder and I advise them to fix. Supposedly they did before mass producing. I decided not to take risk and get for my shop.