It seems that the rumoured imminent release date of iPhone 6 and iPhone 5S will not happen as previous iPhone models remain expensive.

Listings on the online retail giant Amazon, iPhone 5 is still being sold between $700 and $900. iPhone 4S costs around $500. iPhone 5 under a contract bears a price tag that ranges from $99 to $199.

The rumour is fuelled by the speculation that the release iPhone 6 and iPhone 5S will be postponed due to US carrier T-Mobile's delayed availability of the current iPhone. It has been less than a week since T-Mobile announced the long-awaited release of the iPhone 5 on its network free of contract. The smartphone will make its debut with T-Mobile on April 12. Pre-orders for the handset began for the iPhone 5 on Friday.

With the delayed availability of the handset in T-Mobile, Apple may not release the successors of the handset yet. Rumours claimed that Apple is set to unleash iPhone 6 and iPhone 5S in June.

According to Japanese magazine Mac Fan, the new iPhone 5S will be unveiled on June 20 and go on sale by July. It also said the rumoured low-cost version, targeted at India and China, would be launched in August. Mac Fan did not share where it got its news from. However, the new iPhone 5S will not be imbued with Apple's new mobile operating system, iOS7, it would seem.

Some of the rumoured features of the next iPhone are Retina or IGZO screen display, A7 quad core chip processor, iOS 7, 128GB internal storage, 13 mega-pixel camera, and longer battery life. The lack of NFC support on the iPhone 5 was one of the biggest criticisms aimed at Apple's smartphone.

The low cost iPhone 5S, on the other hand, is rumoured to sport a plastic casing, 4-inch screen display, dual core processor and 8-megapixel camera.

As usual, Apple did not comment on the rumours about iPhone 6 or iPhone 5S.