can I use an iphone pay as you go with telus?

Yes,You can do it.
Before use your Telus sim card on your iphone,Make sure your phone is unlocked.
If it's locked means,you will need to unlock it.
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 Unlock-Zone.com and you can get free iphone unlock instructions from MobileUnlockGuide.com