Hi Brian!!
There was a Unication company rep who stated that talk group hold was in the que for the G4 AND G5 but as of this date it has not been implemented.
There is a simple work around though that works real well.On the top of the radio there is a knob that has 8 positions. You can place any p25 system in each knob position and allow it to scan up to 64 talk groups or you can place a single talk group in each of the 8 positions which will allow you to listen and hold on that talk group.
There is the ability to create a zone which will have its own 8 positions. This is done in the menu system of the radio.
I forget how many zones you can have but its allot more than you would ever use.
One of the neat features of the Unications is that you can make your own mp3 or wave audio file and place it on each of the knob positions. So for example lets say you place fire dispatch on knob position 1 the wave file could say fire department dispatch every time you selected the first knob position. This feature would be real helpful to you since your legally blind.
Not that your driving but when I am driving down the road I turn the knob position and without looking at the radio or taking my eyes off the road it tells me what talk groups i am listening to.Very nice feature!!!
I use text to wave program to do this its a free program available from the link below....
https://www.vector.co.jp/download/file/winnt/art/fh698474.html
Tim