I used to be on Fido, have since left them. I am not here to bash them but share experiences.
I upgraded to a 4 from a 3G while on fido. I was very satisfied with my plan ($30 data +$25 voice/text, no other costs) so I decided to line up for a 4 and stick with fido. However, as you know they are on 3 year plans, not 2. Having been only with them for 2 years since the 3G, I called and confirmed that I could infact, upgrade for $299 (32gb) AND use my fido dollars. Score. I lined up, activated, signed new contract and had my phone in my hand out the door. I go online to check my bill in a week or so to check the charges. Fido had decided that since I didnt complete my previous contract, and they were doing me the favor of letting me upgrade early, that they could then still let me serve out my previous contract before starting my new one. So............stacking my plan means that I was in a CONTRACT with Fido, with my iPhone 4, for the next
4 years. No thanks. I paid my ETF ($350) and moved to rogers pay-as-you-go. I still came out on top with a cheap iphone 4, but fido wouldn't unlock my iphone 4 for any reason blah blah blah.

I have used a gevey sim since then.