With the imminent release of Apple's iPhone 5, smartphone users are already selling their old handsets to get money to buy the new iOS device.

According to online trading site, eBay, there is a spike in the number of owners trying to sell their current smartphones. The site reported that smartphone trade-ins increased about 70 percent. The increase is sparked by the reports from credible new websites that iPhone 5 will be launched on September 12 and will be available on September 21.

This is supported by tech devices buyer Gazelle and NextWorth said that there is an increase in number of people selling their handsets on the aforementioned companies.

The companies refurbish the gadgets and sell them online in eBay or Amazon. Gazelle's price for an AT&T 16GB iPhone 4S was $277, while NextWorth, another used smartphone buyer, offered $263 for the same model.

However, the tricky part is when is the best time to sell my old iPhone? That's a question I hear almost every day as the iPhone 5 launch looms.

Knowing the best time to trade in your old smartphones for an iPhone 5 is difficult for most users to take advantage of, especially when we all want to get the best value for our own handsets. According to past sales data, the high price of the iPhone 4S is expected to be two to three weeks before the iPhone 5 is announced.

There is already a dip in the prices of previous models of iPhones. According to NextWorth's chief marketing Jeff Trachsel, the earlier you can sell the better. However, many users said that they wait until Apple announced that a new phone is coming before selling their old handset.

As usual, tech giant Apple is tight-lipped about the features and release date of its latest smartphone. However, numerous rumors emerged surrounding the handset. The latest rumor is that Apple is developing the thinnest iPhone yet. Analysts predicted that we will be seeing a 7.66mm thin iPhone 5.

Taiwanese daily newspaper Apple Daily published a report claiming that the new iPhone 5 will be skinnier. Earlier reports have suggested that the device will be taller than the current model and feature an expanded display.

With minimal changes made on the outside, we can only hope that the Apple packed more inside the new iPhone 5. Some of the rumored features of the upcoming iPhone 5 are 4G/LTE capability, A6 chip and equipped by the new iOS 6.

Another rumor surrounding the device is its smaller micro dock connector. Previous iPhones sport a 30-pin dock connector and earlier reports claimed that it will be replaced with 19-pin dock connector. This may impact consumers who would like to upgrade as they will also have to upgrade their accessories using 30-pin.

New reports said that the new iPhone 5 will have a 9-pin dock connector. The beta version of iOS 6 holds proof on this claim. Smaller dock connector will yield more space inside for greater features.

iPhone 5 is expected to be launched on September 12 and will be available on the 21st.