If you want to put Telus pay as you go plan on your iPhone 4 means,Your iphone should be unlocked one.If it's locked by other than Telus carrier,you will need to unlock your iPhone 4.
For unlocking you can approach your service provider or else try to buy an unlocking service from any one of the online unlocking service provider like ClassicUnlocking.com Here you can unlock your iPhone by Remote unlocking method.It's one of the best and safe way to unlock your iPhone 4 without jailbreaking.