Call transfer to cell phone question!

I need to make cell phone call transfer. but iw ould like to detect if the cell answer or not, so after like 30 seconds i will be able to send it to the voicemail. I know the followme option, but it is not a way i want to do it, is it possible to detect when ring tone stop?? thanx lot! by the way i’m running my asterisk on a linksys router so external modules installation are not really easy thanx!

yes you can do a
Dial(local/5555555,15) the 15 is a timer you can set to whatever
and local is your trunk out

Yes but when i do that, it see the trunk as answered as soon as it ring so the voicemail never answer. i must be able to detect ring or voice.