Use of IPhones in Canada will probably increase significantly in the near future, as Telus and Bell will start offering the IPhone next month. This will also provide a greater degree of competition as Rogers will no longer have a monopoly on these. Until the rate plans are introduced, it won't be possible to determine the degree of savings between networks, but it's possible these will be minimal due to the agreements between each network and Apple (which reportedly prohibits "discounting" between suppliers that carry the IPhone). It will be interesting to see whether Telus and Bell will also insist on "locking" customers into a three-year contract as Rogers does?
Those thinking of upgrading an older technology phone to an IPhone (or other smart phone) should be prepared to pay more, as Rogers has stated that IPhone users spend 1.5 times more than "standard" phone users.
Both Telus and Bell have been overlaying their existing CDMA network with GSM/HSPA technology, so GSM phones will be increasingly available as well. Verizon in the U.S. is reportedly also following the same upgrade path, but it's not clear whether Verizon will adopt GSM or go right to the new LTE technology which will start appearing next year (at least in Europe).
One caveat of course is that Telus and Bell customers travelling to Europe with IPhones should be sure to disable the data portion of the phone so as not to incur HUGE data roaming charges.
Cheers!