If your device doesn’t support radius you can use any hosted softswitch billing systems.The first key question is how many minutes your call traffic.. If you have 30000-40000 minutes call traffic this sytems don’t offer much money for example america is 1 cent, if you have less traffic like 5000-15000 minutes they offer 2 cents for america and 500 $ for per month…I offer you buy a new gateway which supports radius and ivr.. Well known devices are quintum and cisco gateways.. Quintum is cheaper and has easy ios software