asiclly what G3/G4 means it the type of DOC used (Disk On Chip)
Soft reset your Prophet (insert the stylus into the little hole on the bottom of your Prophet (to the left of the mini-USB connector)
When your prophet boots up, it will show you a number of things in red text.
If you look at the IPL and SPL numbers, you’ll see they end in .000 in this case your phone is a G3 model.
So, in short:
IPL/SPL: ending in .000 = G3 model
IPL/SPL: ending in .0000 = G3 model
IPL/SPL: ending in .0001 = G4 model
It is not possible to upgrade from a G3 model to a G4 model through software, as the DOC is a piece of Hardware.
The only noticeable difference between the two is that G3 devices have slightly more available RAM/ROM/