I have done some searching and found something like "dial your VM then put in #30" for example. The number 30 being seconds of ringing before the voicemail kicks in.
I went through the 3 pages of tips and tricks and also searched the Telus site with no luck.
Call your carrier (Telus). I think some GSM carriers can change the setting from their end, but I don't know if the cdma has an equivalent setting the carrier can change.
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When I first started with ATT, my phone would only ring about 4 times before reverting to voice mail. I had to call them and now my phones all ring for 30 seconds. Your carrier should be able to resolve that issue for you.