After purchasing the iPhone 3G S, things went downhill briefly. It turned out that the phone number I picked with my new contract was previously owned by someone under "legal investigation" (at least, that's what the people phoning me said). That, combined with the fact that my previous voice plan was significantly cheaper compelled me to switch the iPhone to my previous plan.
Apparently, the only way to do this was to order a new iPhone (which would arrive by UPS in three to five days), not use the other iPhone more than 30 minutes, and return it to the store. I realized that this was ridiculously inefficient and a strange form of torture (having the iPhone, but not being allowed to use it) but was willing to endure this in order to save the activation fee and a recurring $11 per month.
Of course, when I called five days later to request a tracking number, I learned that the iPhone had never shipped and that they were out of stock.
Fortunately, the reasonable option was now possible: I could activate the iPhone under my existing plan and cancel the new plan. Either the representative was more knowledgeable (she was certainly very helpful -- rather than simply transferring me, she acted on my behalf for both the shipping cancellation and the plan cancellation), or Rogers had a change of heart due to the problems people were experiencing.
In summary, it is possible for Rogers customers to upgrade to an iPhone 3G S and just add a data plan to their existing voice plan. (Perhaps the threat of 3G competition from Telus in October is at work as well.)