Brilliance of the SIM... doesn't matter which phone you put it in if using the same service provider (NEXTEL to NEXTEL, Telus to Telus). Where you get into problems is when you switch between providers (NEXTEL to Telus, NEXTEL to Boost, Boost to NEXTEL, etc.) Unlock codes are only needed when switching between carriers using the same SIM. The matter of you switching the phone you use would not cause a problem. If you took the SIM from the eBay model and tried getting it to work with Telus, you'd most likely need an unlock code before it would work.