HI yes what you said was rite if you buy an unlocked sidekick then sure you can freely use it with telus or any other GSM sim .Else if the sidekick phone is locked to some other network provider then you can't use other network sim in it until you unlock it ...You can easily unlock your phone using sites like Unlock-Zone.com they are providing unlock code for all mobile models at reliable cost ..After purchasing the code visit sites like MobileUnlockGuide.com to get free instruction about how to use that code and unlock your phone .