Try this one:
${caller}^100$={
.*=;choice=$(random,?)
${choice}^[0,1,2,3]$=callto_line_1
${choice}^[4,5,6]$=callto_line_2
.....
}
Or you may use the index function (it will choose the target by incrementing a variable):
[$once]
line_index=1
[default]
${caller}^100$=line/123;line=$(index,$(line_index),line1,line2,line3)