UPDATE: We have a winner. Apple announced Monday that the correct answer was “over four million,” the guess of nearly 23% of our readers.

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When the iPhone 4 went on sale 16 months ago, Apple (AAPL) sold 1.7 million in the first weekend, counting pre-orders.

The analysts who have ventured a guess seem confident that by Sunday night, iPhone 4S sales will have smashed that record, but there’s considerable disagreement by how much.

Here are the predictions we’ve seen:

• Piper Jaffray’s Gene Munster: 2.0 to 2.5 million
• RBC Capital’s Mike Abramsky: nearly 3 million
• Yankee Group’s Carl Howe: 4 million

What’s your estimate?

[polldaddy poll=5585941]