Have an SL1100 and can't get the programming to do as expected, on the dial action table I need "2" to cause a group of 3 extension to ring, cannot get this to work, seemed easy on the DSX40.

I like using virtuals.
In the dial action table assign 2 as UTRF to 201
Assign 201 to each of the 3 extensions
Program virtual to ring to the button its assign on, again on each extension.
Virtual does not have to be programmed on a physical button.

It appears that the virtual extensions start at 250 on firmware R7? I can find that and assign the button, but I'm unable to find a way to add the button without programming it onto a physical button?

You are correct virtuals begin at 250
What button phones do they have?

If they have 12 button phones you can assign the virtual on button between 13 and 24, If they have 24 button phones you have to use a existing button.

bingo, found that once I went to advanced, what about the part of assigning the virtual to ring on the button?

Expand 15 (extension setup) look for virtual extension ring assignment. The rest I'll let you figure it out, to me that's the fun part. Trial and error makes one learn quicker.