Well, if you're planning on getting a contract, then there are no savings to be had AND paying full price for a phone stings some more.
If this is your first phone, then I'd recommend seriously assessing your needs before commiting to a 3yr plan; those of us that don't yak a lot can save money using the paygo (voice) option. It certainly gets more complicated and expensive if you want/need a data plan, but in my case, wi-fi is OK and I'll eat the (current) $3/day charge in the event a dire need should arise.
Looking at Rogers website, the cheapest voice+data "personal" plan is $50/mo + SAF and other fees; leading to a bill of $60+ per month
A subsidized 32GB 3GS runs $299, adding $60x36 commits you to spending $2,459 over the life of the contract, assuming that you don't exceed voice/data allowances. Buying your own phone in this case probably adds another $300
On the paygo option, I buy the phone @ $600 and spend ~$100 per year on voice/data for a total of $900, thus saving;
- ~$500 per year (for 3yrs) vs. subsidized phone on a post-paid plan.
- ~$600 per year (for 3yrs) vs. full-price phone on a post-paid plan.
FWIW, I learned these painful lessons after getting my wife a Bell 3yr plan only to learn that she used 10-20 minutes a month. That's expensive talk time