Slight:
You have nothing to worry about. GSM is completely controlled by the SIM card. Just pull out your international SIM (if Telus put it in there; if not, remove any other SIM that might be in there), put in the prepaid SIM, and you're good to go. I've used my TP2 in Dubai and Iran with Sprint none the wiser. It looks like Ireland doesn't even have CDMA up and running yet (
CDG : Worldwide : Worldwide), so there's simply no chance they'll see the CDMA radio. All they'll look for is your SIM, and when you put the prepaid in, that's all that ever shows.