I suspect the perpetrators (that's a surprisingly hard word to spell on a Friday night, if you follow me) figured that since xyz exchange in a particular area (like 902-877 in Halifax) was opened up for Telus phones, they could easily lead people to believe that the message is legitimately from their provider, since it's named.
But it would be amusing to people who have since ported their phone numbers to other providers. You could now be a Rogers or Bell customer and you'd still get this message, if my supposition of how the scam works is correct.
Anyway, Telus knows about this scam. I think they should go out and proactively warn their clients about it, though. I can see why they'd have a disincentive, because they don't want their paying customers to think, "What, you mean I'm not getting a reward for subscribing with Telus?!" But they should swallow their pride (if that is the impediment) and get the word out there.