[macro-replace]
; replace arg2 with arg3 in arg1
; NOTE: ARG2 and ARG3 *must*  be the same length!
exten => s,1,SetVar(Repl_field=1)
exten => s,2,Cut(Repl_new=ARG1,${ARG2},1)
exten => s,3,SetVar(Repl_dst=${Repl_dst}${ARG3}${Repl_new})
exten => s,4,SetVar(Repl_field=$[${Repl_field} + 1])
exten => s,5,GotoIf($[${LEN(${Repl_dst})} <= ${LEN(${ARG1})}]?2)
exten => s,6,SetVar(REPLACED=${Repl_new:1})