With just hours to go before the iPhone 3G S reaches its stores, Canadian provider Rogers and its sister brand Fido have promised heavy discounts for existing iPhone 3G customers trading up to the faster model.

Also, Apple stores in the country will finally let customers buy the devices there instead of carrier stores.

Rogers’ and Fido’s price reductions depend heavily on when customers bought their phones and how much they spend per month on service. The most privileged are those who bought an iPhone 3G before September 30th and who spend at least $100 CAD a month on their total service plan; these get a full subsidy and pay the same $199 CAD for a 16GB iPhone 3G S, or $299 CAD for a 32GB version, as customers new to the service or who qualify for a full upgrade.

Those who spend less than $100 per month but who still bought their iPhones before the end of 2008 get a partial discount. Here, the 16GB iPhone 3G S costs $449 CAD while the 32GB version costs $549.

Additionally, those specifically on Fido can use their FidoDollars to help cover the cost of the iPhone 3G S at any price and get $100 in FidoDollars without having to extend or renew their contracts.

Rogers paints the gesture as its way of rewarding early adopters and says it’s offering existing customers a dramatic discount even though they would normally have to wait up to two years to qualify for the full price. It says those who don’t qualify for any upgrades or as new customers will pay exactly what the carrier does: $680 CAD for a 16GB model and $780 CAD for the larger capacity.

If true, this sets the at-cost US prices of the 2009 phones at about $600 and $700 respectively. The holdover 8GB iPhone 3G will cost $580 CAD (about $514 US) but won’t have an early upgrade option.