iPhone 5 Release Date: iPhone 3GS Users Likely to Upgrade to iPhone 4S

The iPhone 4S may turn out to be a lot more popular than initially expected with analysts projecting that approximately 18.8 million iPhone 3GS users will upgrade to the fifth-generation Apple smartphone.

Many iPhone users went the economical route during the release of the iPhone 4 in 2010 and bought its predecessor the iPhone 3GS for a discounted price before the 4 was released.

Piper Jaffray analyst Gene Munster projects that approximately 27.6 million iPhone 3GS users who bought their smartphone before the release of the iPhone 4 are now ready for an upgrade.

He estimates that 25 percent of those users will also be economical and upgrade to the iPhone 4, which since the unveiling of the iPhone 4S has seen a price cut to $99 for the 8GB model.

The 16GB and 32GB models have also been discounted to $149 and $199 respectively, however once those supplies run out, only the 8GB iPhone 4 will remain available.

Munster estimates that 15 percent of iPhone 3GS users will switch to an Android smartphone.

Android is known for its vast selection of smartphones. Many suggest that Android keeps a variety of phones available to match the demand for the iPhone.

Android smartphones like the Samsung Galaxy S2 and Motorola Droid Bionic are especially popular alternatives to the iPhone. The Galaxy S2 is been called "iPhone Killer."

Munster sees the remaining 18.8-million iPhone 3GS users upgrading to the iPhone 4S.

While many are not impressed and are considering the iPhone 4S simply an upgrade of the iPhone 4, the smartphone has also been recognized for its more notable specs such as its 8MP camera and its exclusive feature, the virtual personal assistant, Siri.

The iPhone 4S will be available for shipping and purchase on Oct. 14.