It's free if you change it online, but Telus recycles numbers so quickly, that if you change your number using the drop down menu online, you'll more likely than not get stuck with another person's credit collection calls, and end up having to change your number again, only to have the same issue. Having suffered that too often, a few years ago I paid the 35.00 fee and got a fab custom number without any harassment attached to it. It's worth it.
Telus holds onto numbers for 90 days. Seems like an appropriate amount of time to me. It's the industry standard. They can hold a number for as long as they want. It doesn't erase the past associated with it. They still have no idea when they are giving a number out if it was used by a drug dealer, someone in debt or a grandma who didn't make many calls. I personally can't come up with a better screening system that doesn't cost a ridiculous amount of money and time. If anybody else can by all means put it in the idea section of the forums.