In its most successful product launch ever, Apple announced it has sold 1.7 million iPhone 4s in the first three days after putting it on the market in several countries, the Kansas City Star reported yesterday. In 2009, Apple sold 1 million units of its 3GS iPhone in the first three days.

However, even some people who pre-ordered the smartphone have had to wait, as Apple had to delay in-store sales to fulfill its preorders first. Seventy-seven percent of buyers queueing outside stores in the first few days were upgrading to the iPhone 4 from previous models, according research from U.S. analysis group Piper Jaffray and UK firm AQA. This means 23 percent of buyers are new to the iPhone, MediaGuardian noted.

"This is confirmation that Apple has another hit. Apple is competing with Google, which seems to have a new Android phone from another partner out every two weeks. Apple gets one chance a year to launch a new phone, and they hit it out of the park," Gene Munster, an analyst at Piper Jaffray, told USA Today.

New features on the iPhone 4 include video calling, 960-by-640 resolution, multiple apps usage, and HD video recording, according to Apple.