Custom ring tone

i tried to implement custom ring but double ring tones (custom and called channel’s ringtone) are both heard before one answers. According to manule, “no audio from the called channel(s) until one answers” for opton ‘r’ and ‘m’

cisco as5350 -> asterisk 1.4.0 (sip) -> as5350

exten => 2118,1,Wait(1) ; Wait a second, just for fun
exten => 2118,2,Answer ; Answer the line
exten => 2118,3,SetCallerPres(unavailable)
exten => 2118,4,dial(sip/492362@,40,m)

pls advise