You can get the hardware upgrade to an iphone , but without signing a data plan, your going to be paying a higher cost than the advertised 199 or 299 price they advertise.
If you choose to pay for the phone and sign the contract with out data, you can just switch your sim over and use the phone. To block data just call in and request them disable any type of data on your phone.
If you want data , you have to sign a SEPARATE 3 year agreement on data, so you will have 2 3 yr contracts with rogers. There is no other way to add data unless you sign the contract.
Since you dont want data, what I would suggest is to either Buy the phone outright from rogers since they have it available for pay as u go customers. OR just check kijiji and stuff for one that is either used or new (its still expensive but you save money doing it this way than to buy it brand new, a lot of people do hardware upgrades and sell the phone for extra $$)
You can check kijiji classified or howardforums classifides.
So in your situation there will be no point of you resigning a 3 year agreemenbt and almost paying how much the phone is worth when you can avoid an agreement and find the phone else where.
I had my iphone on pay as you go for over a year now. It works fine for me, and there is no 3g ... but for some reason my edge works and i dont get charged for me ..