Consumers buying the unlocked iPhone 5 are making a wise investment move, a new report said, amidst indications that the Apple flagship's price mark is plummeting at an accelerating rate as the iPhone 5S release date nears.

According to investment banker Piper Jaffray, the iPhone 5 that Apple had released in September represents not only a good buy but also a prudent investment move.

Compared to Samsung's 2012 flagships - the Galaxy S3 and the phablet Galaxy Note 2, the iOS 6 smartphone fetches higher value when put up in the pre-owned gadget market, the Piper Jaffray report said.

The Apple handset only loses 11.2 per cent of its original value while that of Samsung's gives up 13.7 smartphone, offering the possibility that unlocked iPhone 5 owners will be able to attract high asking price the moment they decide to upgrade and get the upcoming iPhone 5S, Piper Jaffray analyst Gene Munster said in a report.

"The key takeaway from 8 weeks of data is that the iPhone is holding slightly more of its value compared to the top two Galaxy phones," Mr Munster is reported by Apple Insider as saying in a report.

He noted that the data is confined to iPhone 5 users located in the United States.

The report also highlighted the impressive ability of older iPhone models in retaining their value. Surprisingly, the iPhone 4S came out as the better performer, shedding only seven per cent of its value.

The iPhone 4, on the other hand, discards eight per cent, besting even the Note 2 that suffers a value retreat of 15 per cent after only two months of coming out of the box.

Among the three, the iPhone 4S emerged as the best buy for consumers. In fact, its value is that high that U.S. carrier AT&T is willing to accept the 4S in a trade-in scheme that allows consumers to get the iPhone 5 for free plus a two-year contract.

According to Apple Insider, the promo is limited to current AT&T subscribers seeking to upgrade to the next level. They must ensure, however, that the 4S they'll be presenting is "three years old or newer and in good working condition."

What they get in return is a 16GB iPhone 5 minus the need of paying $US199 upfront. To come with the contract are choices of plans that require monthly bills of between $US20 and $US85 plus access to a fast 4G network.

Lately, the iPhone 5 has become the subject of sizeable discounts from U.S. telcos, a trend that experts said will continue as the supposed 2013 release date of its replacement, the iPhone 5S, nears.

Verizon has an ongoing promo that dangles the iPhone 5 for only $US99 while T-Mobile also pushes for a trade-in program that uses zero initial payment as the main come-on.