Those 1 million iPhone GSs sold last weekend represent a “remarkable achievement,” writes RBC Capital’s Mike Abramsky in a note to clients issued early Tuesday, especially considering the new iPhone’s relatively narrow international distribution (8 countries vs. 21 last year).

But according to Abramsky, it’s the old iPhone 3G — newly priced at $99 — not the new 3GS, that will drive global sales this fiscal year.

“While early buyers appeared to favor the iPhone S,” he writes, “the $99 iPhone is expected to drive 30-40% momentum improvement, in countries like UK, Germany, France, and other parts of Europe and Asia where phones are more highly subsidized (on contract) and prepaid is popular (e.g. ~60% prepay in UK, ~90% in emerging markets like India).”

Abramsky expects Apple to sell 20 million iPhones in fiscal 2009, 64.5% of them the older 3G models. By his estimates the new 3GS won’t dominate sales until fiscal 2010, when he expects Apple to sell 30 million iPhones, roughly 60% of them 3GSs. See chart and spreadsheet below.

On Monday, Apple announced that it sold 1 million iPhones 3GSs in three days of sales. The company has not released the number of iPhones 3Gs sold since that device’s price was lowered to $99 from $199 on June 8.