Try this suggestion from the Koodo forums:
1- Dial *#61# on your device. It should say something like this:
Call Forwarding
Voice: +########## after XX seconds
The "+###..." is the number that calls are forwarded to- write this down. The "XX" is the amount of time a caller has to wait in seconds.
2- Dial **61*+##########*11*XX# with "+###..." being the number you wrote down, and "XX" being the new amount of time. Note that the amount of time can only be increased/decreased in 5 second intervals, i.e. you can enter "15" but not "26". You should get a "Network Message" saying something like this:
Call Forwarding
Registration was successful
3- Everything should now be set up! You can check by dialing *#61# and seeing how much time the caller has to wait, or calling the device and seeing how long you wait until voicemail.
Highest duration I could achieve was 30 seconds the default was 25 seconds which was 4 rings, now it's 6 rings before calls go to voicemail. Stock ringtones were used in this test using an HTC Raider. Results may vary.
NFtoBC
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