The BlackBerry 7520i for Mike uses a completely different network (iDEN) than other Telus devices (CDMA or HSPA). It requires an activated SIM card to utilize any voice or data services. Telus Client Care should be able to do a device swap for you if you provide them with the BlackBerry PIN (or IMEI) and the SIM ID.
I've always had a Mike North America plan, so someone else will have to comment as to whether a Mike device can be activated using a non-Mike rate plan (which I presume you currently have). That being said, the Mike plans, especially for North America, can be quite competitive. I'm sure someone in Client Care should be able to answer that fairly quickly, though (and maybe even courteously if you catch them on a good day).
Keep in mind that Mike is great for push data (like BlackBerry email), but it's a slower 2G technology, not 3G like EV-DO or HSPA.
We don't care. We don't have to.
We're the phone company.