Apple is gearing for its widely-anticipated launch of its latest iPhone 3G S on Friday leaving analysts speculating on how the handset will perform in terms of sales.

Piper Jaffray's senior analyst Gene Munster thinks it's going to be a good weekend for Apple and AT&T as it estimates they will sell 500,000 iPhones this weekend, according to a research note sent to clients, reports Fortune.

The estimate is half as many phones as Apple first sold when it launched the iPhone 3G. But to put that into perspective, Apple sold launched the first iPhone in 21 countries on the first day. In comparison, the iPhone 3G S will be sold in only eight countries on its first day.

Still, 500,000 phones sold in three days is a lofty number. Consider that the iPhone 3G was a fairly big upgrade over its predecessor when it was released, and most notably added the much faster 3G data speeds to the device.

The new iPhone 3G S, which the company says is the fastest iPhone ever, comes with a 3-megapixel camera and can record video. Other features include voice recording, spotlight search, compass among others. The handset will also have iPhone OS 3.0, the new software that apple released on Wednesday.